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Public Secret Message

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If you're wondering where they're reading the words from, it's in Morse code, on the rings around the owls.

Alice needs to send a message to Bob without Eve overhearing. Unfortunately for Alice, she can't simply meet with Bob in private to discuss it, and sending a private message is either physically impossible or would arouse too many suspicions. The solution? Send a message to everyone, but encode, encrypt, or word it in a way that only Bob will understand the message. Alice might disguise the message in such a way that Eve will think it's a relatively innocent item, such as an advertisement (Wikipedia lists this technique as "Steganography"), worded so that everyone but Bob will misinterpret the meaning, or simply make the message so hard to decode that only Bob could do it.

Subtrope to Double Meaning. Supertrope to Talking through Technique, Covert Distress Code, Code Emergency, and Trouble Entendre. Compare/contrast Sarcastic Confession, Hidden in Plain Sight, Overt Rendezvous, Deception Non-Compliance. May overlap with Spy Speak and Cryptic Conversation.


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    Anime & Manga 
  • Case Closed: In the two-part episode "The Secret of the Sun, Moon and Stars", Professor Agasa and Conan Edogawa suggest that the drawings of the sun, moon, and stars found on various objects in the home of Agasa's late uncle were a code much like the Dancing Men from Sherlock Holmes.
  • The ComiQ: The protagonist, Ryota, discovers that the anonymous background artist for his manga is in fact a man framed and imprisoned for a murder from three years prior. As the prison prohibits this background artist from expressing himself to the outside world in any other way, he has to communicate to Ryota about what he knows about the murder through signs and symbols embedded into Ryota's manga's backgrounds.
  • Dance in the Vampire Bund: At one point, Mina makes a public announcement, speaking in ancient Sumerian as a challenge to another vampire, but with fake subtitles in Japanese.
  • Death Note: Misa is a Kira-fangirl, but doesn't know who he is. So she uses her own Death Note to kill people and force the news to send messages. Light is annoyed, since while people who don't know about the notebooks won't be able to figure out what they're talking about, it is still far too public for his taste.
  • Fullmetal Alchemist: Riza Hawkeye uses this to deliver a message to Roy Mustang while she's under surveillance. She gets into a mundane conversation with him over lunch in which she talks about the activities of various people she knows. Mustang is later able to take the first initial of each name Hawkeye mentioned and spell out her message: SELIM BRADLEY IS HOMUNCULUS.
  • In The Kindaichi Case Files, Takato frames Kindaichi of stabbing Superintendent Akechi in order to break his spirit. Akechi manages to survive because the true culprit—who is Takato's Unwitting Pawn—made a mistake. To drop the villains' guards however, Akechi feigns his death and writes an orbituary on himself with a hidden message in the article, telling Kindaichi that he's still alive.
  • Monster: Tenma needed to speak with a former college classmate, so he put an ad in the paper that simply said "Let's discuss our memories of cheating", a reference to a test at medical school that the two happened to discuss the last time they ran into each other.
  • My Hero Academia: The secret investigation involving The Mole, Hawks, who has infiltrated the League of Villains and has discovered that they have massively swelled their numbers by taking over the Meta Liberation Army and now have the strength necessary to take on all the heroes and destroy Japan. The Public Safety Commission can't let anyone know about any of this for fear of moles in their own ranks. Despite this, both the Comission and Hawks manage to secretly get the word out in two ways:
    • The Safety Commission requests that U.A. restart their student hero internships ahead of schedule, the heavy handed manner of the request, which makes it more of an order than an actual request, clues the U.A. staff into quickly (and correctly) deducing that the Commission has secretly discovered that a major crisis is about to unfold and they need every possible hand on deck to combat it.
    • Hawks can't directly tell anyone else what he's doing and what's going to go down for fear of being compromised, but he is able to give Endeavour the manuscript for the Meta Liberation Army, and tells him to take a look at it sometime, particularly the sections he personally highlighted. Endeavour notices that something is off about Hawks from his changed demeanour and after reading through the highlighted sections, discovers that the second word of each highlight assembles a covert message warning him that the endgame approaches.
  • One Piece: At the end of the manga's fifth saga, the main character returns to the scene of a major battle, ostensibly to honor the dead. Reporters on the scene photographed him, and his crew, scattered around the world, saw the article, and realized it wasn't the kind of thing their captain typically did, and noticed a simple message written on a tattoo. Meanwhile, the World Government were too fixated on trying to figure out what hidden message there might be in the number of times he conspicuously rung a bell in front of Marine HQ to even notice the two letters and two numbers on Luffy's arm, let alone figure out what they meant. Which would've still been rather hard to figure out without context that only the Straw Hats themselves and a handful of their closest allies would know.
  • The Promised Neverland: Books shipped into the orphanage by William Minerva contain hidden messages to inform the kids of the orphanage of the true nature of the world outside while slipping past Isabella's vigilant security:
    • The first messages discovered are contained within the stamps on the inside front covers: The stamps, which depict Minerva's owl emblem, have imperfections on the rings that look like the results of hand-stamping but actually form dots and dashes to create words in Morse code—putting the books in chronological order of publication creates a message urging the kids to escape as the place is actually a farm run by demons who want to harvest and eat them.
    • A number of his books are also adventure novels, which turn out to be guides on how to deal with, escape from, and fool monsters and other dangerous creatures that live outside of the orphanage.
    • One book's Morse code stamp does not seem to fit with the others, being a seemingly random bunch of numbers. By looking through the books themselves, namely their page numbers and the order of the words on those pages, they discover it's the password for a pen smuggled into the orphanage that unlocks its GPS capabilities, which displays locations in a coordinate system that only Minerva uses that the kids also have to figure out. Within the box the pen came in is yet another encrypted message, telling the kids his location (in those coordinates) and to find him if they ever need help.
  • Summer Time Rendering: In order to keep her whereabouts and identity a secret from the shadows, Hizuru encrypts her contact info with a code that can only be deciphered using her real name and her pen name. At this point in time only she and Nezu have both of these pieces of information, so by Hizuru's logic the only other person who could crack the code should be the time traveler she is searching for.

    Comic Books 
  • In Strangers at the Heart's Core, a criminal group called the Visitors coerce Fred Danvers into sending Supergirl a holographic message to dissuade her from searching for their headquarters. As listening to her father's projection warning that her mother is being held hostage, Supergirl notices how peculiarly and insistently he is stressing "[She] cannot go past [him]" because "It's a stone wall before [her]!". Given that there are no walls around her -because she happens to be flying over the Catskill Mountains-, Supergirl realizes he is surreptitiously saying he can teleport her into the Visitors' lair if she flies into his hologram.
  • Tintin: In 1934 Hergé drew a story named The Blue Lotus in which Tintin travels to China. Hergé's friend, a Chinese foreign exchange student named Zhang Chong Ren told him a lot about Chinese culture and society, including the then current situation in Asia, where Japan had military occupied China. He also wrote all the Chinese signs, billboards, ideograms and texts seen in the backgrounds. As a Bilingual Bonus only Chinese people could read these. This also might explain why the book wasn't censored from the start because many of these texts are anti-Japanese slogans, like for instance: Boycott Japanese products, Abolish unfair treaties and Down with Imperialism. Upon realizing the anti-Japanese tone of the story, Japan's diplomats stationed in Belgium issued an official complaint and threatened to take their complaint to the Permanent Court of International Justice at The Hague. Zhang congratulated Hergé, stating that it would only further expose the actions of Japan in China to further international scrutiny and would make Hergé "world-famous".

    Fan Works 
  • Checkmate (Anla'Shok): During the 3rd Quarter Quell, Cashmere wounds Beetee at the Cornucopia while screaming "Where is your plan now, genius?" Only Plutarch and the rebel tributes within earshot realize that her rebuke is actually for the rebels who had earlier promised her that they would rescue all of the tributes but didn't keep that promise.
  • In Double Agent Vader, one of the ways Anakin relieves his feelings is by anonymously sending an elaborate flower arrangement to the annual gala celebrating the founding of the Empire, using the Naboo traditional flower language (which Anakin learned from Padme, and which is one of many Naboo traditions Palpatine never bothered to learn) to say exactly what he thinks of Palpatine. The senator from Naboo also knows the flower language, and gets a certain amount of surreptitious pleasure from decoding the message each year — and finds, one year, that it also includes a message to her, warning her of Palpatine's plans to dissolve the Senate and crack down on suspected rebel sympathizers.
  • In Purple Days, Joffrey finds a mysterious cypher that he knows for a fact was meant for him and him alone. It turns out to be a double cypher: first, each symbol represents a different letter, correlating to constellations and the different number of stars on each, and the second uses a clue found in Yeen, "everyone but the purple prince steps to the right" - telling Joffrey to move each letter except those in his name one position to the right, finally producing the message.
  • In Chapter 23 of This Bites!, Cross utilizes the SBS to send a coded message to Sabo, phrased so that nobody other than his brothers and the Revolutionaries could discern its recipient, to tell him about his brothers.
  • Vow of Nudity: While at dinner with the king, Haara is quizzed on the Genasi national symbol. After she discusses the four elemental colors and nuances of the design, the King seems to accept her answer. But later, after she's truly pissed him off, he brings up their prior discussion to point out there's a fifth color; black, the border color that surrounds and shapes the other four, like the Void Genasi do for the empire as a whole.
  • In The Warcrafter, Adrian manages to warn Armsmaster about Calvert's Secret Identity as Coil and his power without the villain learning about it by hiding it under a combination of really loud music and making just enough statements out loud to make it seem like there's something else running.

    Film — Live-Action 
  • In Amélie: When Amélie and Nino are described as the childhood friends that never were, the young Amélie and Nino are seen flashing lights out of their windows at each other.
  • In Angry Video Game Nerd: The Movie, the Atari Eee Tee games have a level design emulating Area 51.
  • The Art of War (2000). A female agent is shown printing posters for a Lost Cat, even though said cat is in her room. She's murdered before she has a chance to put the posters up, but the protagonist finds them in her apartment and deciphers the message encoded in each poster.
  • In the original script (not the final script) of Back to the Future Part II, Marty gets lost and arrested in the 1960s. Without any ID he can give the authorities that wouldn't reveal him as a time traveler, he gives his name as "Marty DeLorean" and tells his lawyer to publish his story in the newspapers, in the hopes of Doc Brown discovering the newspaper and bailing him out. It doesn't quite go as planned, though: while Doc does see and recognize the message, Lorraine (a hippie in this time period) gets to him first and bails him out, believing him to be a kindred spirit (apparently not noticing that he looks identical to her one-time boyfriend "Calvin Klein").
    • A probably-less-deliberate example happens in the game series (see below).
  • Don't Talk has the FBI trace a spy ring working for the Japanese to a diner, but they can't figure out how the waitress at the diner is getting the intelligence out to her co-conspirators. It turns out that she rearranges the letters in the menu sign posted in the front window. The other saboteurs have a sheet with holes cut out into it, which, when laid over a picture of the sign, reveals the secret info hidden within.
  • The Gauntlet: The Mafia keeps track of The Bet about whether witness Augustina "Gus" Malley will make it to the trial on Phoenix via a made-up horse race and a made-up horse called "Malley No-Show".
  • In Get Smart, KAOS turncoat Dalip is able to tip off Max to Siegfried's plan via a cryptic request on American Top 40, playing on Dalip & Max's shared love of Ryan Seacrest.
  • In Hackers, Crash Override is arrested while holding a floppy disk with important, incriminating information, but manages to slip the disk into a trash bin. When taken outside, he sees his ally Cereal Killer in the crowd and goes off on a rant, "They're TRASHING our rights, man! They're TRASHING the flow of data! They're TRASHING!...." Cereal gets the message, and is next seen rummaging through the trash bin.
  • The Ipcress File. Harry Palmer tries to negotiate a trade with a villain. In reply he's given a flyer with a phone number written on it and told to call at a particular time. Harry however dials the number straight away and is told by the operator that it doesn't exist. Realising he's been fooled, he chases after the villain only to be beaten up by his bodyguard. Harry returns to his boss and admits defeat, whereupon he's told to look at the flyer — advertising a public band performance where the villain is in fact waiting.
  • A variation in I, Robot with Dr. Lanning's hologram. It doesn't say much of use while in public, but the whole point was to alert Det. Spooner without anyone else noticing.
    • Even more understandable and closer to the trope when you realise that Lanning couldn't simply encode the answers into the hologram because he was being constantly watched at the time, so he encoded the hologram with a "that's the right question" response and had it respond with that whenever Spooner's question indicated he was on the right track to solve the mystery.
  • In the Journey to the Center of the Earth film sequel, Journey 2: The Mysterious Island, Sean receives a radio signal with each word being characters of Jules Verne. With his stepfather's help to discover to be a Morse Code that the island is real and able to get the coordinates by combining the maps from Treasure Island, Gulliver's Travels, and The Mysterious Island.
  • In Kingsajz Adaś needs to improvise a way to tell Olo the secret formula for the titular Magic Potion, which he does by stringing together chemical symbols in a way that makes them sound like words. All this accomplishes is making the protagonists' task harder, because the bad guys do know the formula already.
  • Appears in both Manhunter and Red Dragon. The imprisoned Hannibal uses personal ads to communicate with Francis Dolarhyde using a book cipher. In the former, the ciphered text is a copy of the Baltimore criminal code; in the latter, it's The Joy of Cooking.
  • In Men in Black, tabloids, which are assumed to be hoaxes by muggles, are in fact based on true events behind The Masquerade (since tabloids have less Weirdness Censor than "serious" newspapers; the New York Times gets lucky...sometimes). Later, when agent K retires, Agent J notices an article with Agent K's photo and an article about a postal worker who returned to his old job after years in a coma, revealing Agent K's fate, which then becomes a major plot point in the second film.
  • In Mercury Rising, a secret agency publishes messages in secret codes in the puzzles section of newspapers to determine how difficult they are for amateur code crackers. When a nine-year-old autistic boy solves one thought to be particularly secure, conflict ensues between factions with opposing ideas about what to do about it.
  • Reservoir Dogs: In the film Mr. Brown explains what he thinks is the hidden message in the lyrics of Madonna's song Like a Virgin.
  • In Serenity, the code that makes River flip out is hidden in an ad spot for Fruity Oaty Bars.
  • A Simple Favor: Stephanie twice uses her vlog to covertly send a message to Emily. The first time, she makes a vlog about how she feels Emily "isn't truly gone," and how she feels close to Emily, "almost like a twin." Emily, who's watching, immediately realizes that Stephanie knows she's alive, and that she has a twin sister. The second time, Stephanie says that she's going to pay tribute to Emily by going to her grave the next morning to make her favorite drink. Sure enough, Emily shows up at her own grave, finds Stephanie waiting for her, and the two have a little chat.
  • In Star Trek II: The Wrath of Khan, Spock tells Kirk on an open channel, "If we go by the book, hours could seem like days". To anyone else, this might sound like a case of Lawful Stupid, but Kirk, who'd been discussing regulations about coded messages with Spock earlier, knows that this means to decode the next message, replace the word "days" with "hours".
  • Wag the Dog: One part of the story regarding the soldier Schumann (a fake American POW for a fake war in Albania) is a photo of him in captivity with his sweater ripped in a pattern that "turns out" to be a Morse Code message saying that he's okay and asking for his mother to stay strong.



  • Agatha Christie
    • In one book, she wrote of a spy who was behind enemy lines and managed to find a really crucial piece of information but had no way of passing it on, so in the end he sacrificed himself, committing a series of murders and getting convicted — it seemed like random acts of violence but those who knew he was a spy figured that the victims' personal data was used as a code.
    • In one of the Tommy and Tuppence stories, Tommy is able to tell Tuppence "These new clients are suspicious. Contact our police liaison and follow me when I go off with them" right in front of the clients, by disguising it as an order for dinner.
    • In the short story "The Four Suspects," a German terrorist organization called the Schwartze Hand is destroyed by a man named Dr. Rosen. The remaining members are out for his blood, so he heads to England to hide, living in a randomly-selected village with four other people—the titular suspects—in the house. When Dr. Rosen is murdered, Scotland Yard correctly deduces that the Schwartze Hand sent a signal to someone in the household who was serving as a mole for the group. They suspect a letter riddled with spelling errors and grammatical mistakes to be that message, but it's actually another letter received the morning of the murder, which contains several capitalized words: Dr. Helmut Spath, Edgar Jackson, Amos Perry, Tsingtau, and Honesty. These are all dahlia variants, and the initial letters spell DEATH.
    • In one short story, a woman discovers that her husband has a habit of murdering his wives. She can't signal for help because he's sitting in the next room, so she telephones the local butcher's and pretends to be placing an order. During the call, she covertly presses down on the receiver at different points, so only certain words get through: "I need help"—press—"with a party I'm having, so"—press—" please come at once"—press—"with some beef; I know it sounds silly, but it's"—press—"a matter of life and death"—press—"that this party goes well..." Her husband is a bit suspicious, but she plays it off as simply being overly dramatic to get better customer service, which he accepts.

Individual works

  • In Anne of Green Gables, Anne and Diana signal to each other at night, using their bedroom candles and cardboard to send a certain number of flashes. When Diana sends a "come at once" signal, Marilla is not impressed by this use of candles, fearing a fire.
  • In The Anubis Gates by Tim Powers, time travelers in the early 19th century get each other's attentions on busy city streets by whistling Beatles songs.
  • In Brotherhood of the Rose by David Morrell, a CIA agent is apparently calling his contact via a public phone booth, but is actually reading a line of graffiti written on the wall of the booth as a coded message.
  • In the Ngaio Marsh novel Death in a White Tie, one partner in a blackmail scheme sends a coded message to his accomplice via a personal advert in a newspaper: "Childie Darling. Living in exile. Longing. Only want Daughter. Daddy." Taking the first letter of each word yields C.D. Lie low. D.D. [To]Columbo Dimitri Lie low. [signed] Daniel Davidson.
  • In the Young Bond novel Double or Die, Bond's teacher (who is also a cryptic crossword compiler) is kidnapped. The kidnappers allow him to submit his final crossword as failure to submit it would have alerted people to the fact he was missing. He uses the crossword to conceal clues as to his location.
  • In The End of Eternity, a stranded time traveler publishes an advertisement in a newspaper containing a picture of a mushroom and the phrase:
    All the
    Of the
    • While this means little to locals, the stranded time traveller knows that Mission Control in the future has a large collection of 20th century advertising. The atomic bomb anachronism tells Mission Control where and when he is.
  • In John Twelve Hawks' (a pseudonym) The Fourth Realm trilogy, this is how the Harlequins communicate with each other and with Travelers. They leave graffiti or other notes in public places that have easily detectable second meanings decodable only by other Harlequins or Travelers.
  • Robert A. Heinlein's novel Friday. In Vancouver, Friday is reading the personal ads in a newspaper and sees an ad that says "W.K.-Make your will. You have only a week to live. A.C.B." More than a week later she sees another ad in a Vicksburg, Mississippi newspaper that says "W.K.-Make your will. You have only ten days to live. A.C.B." Her traveling companion Georges realizes that the messages are a code — the first message meant "number seven" (1 week = 7 days), while the second message meant "number ten".
  • In Giants' Star by James P. Hogan, Vic Hunt needs to send a secret message from Earth to his friend Joe Shannon on board the distant spacecraft Jupiter Five, when Shannon doesn't even know to expect such a message, let alone how to decode it. Hunt sends a plaintext email that subtly directs Shannon to specific answers in that day's newspaper crossword puzzle. The original email alone means nothing, the crossword puzzle answers are just crossword puzzle answers, but when they're combined, they give Shannon instructions that lead him to the real message, which is buried in a bunch of data files also sent from Earth.
  • In Harry Potter and the Order of the Phoenix, Harry alerts Snape while making it possible to convince Umbridge he was shouting gibberish, by yelling "He's got Padfoot at the place where it's hidden!" to the entire room. Snape understands that "Padfoot" was Sirius' old nickname and "the place" was a location that Snape knows Harry's been seeing in his dreams.
  • Heir to the Empire:
    • A variation is used: Mara Jade needs to send a message to her boss, Talon Karrde, but there's no way to do so without the message being intercepted by an Imperial Star Destroyer in orbit. Luke Skywalker (who is with her at the time), suggests using a "counterpart encrypt" between his astromech droid (also with them) and his X-wing (in Karrde's possession). The unusual encrypt works; the X-wing's computer decodes the message easily, while everyone else is stumped by it (although the Empire, while unable to read the message, does at least manage to figure out that the message is using a counterpart encrypt). While this does leave the Empire suspicious of Karrde, they're not that suspicious because they know he's a smuggler and his subordinates might have any number of things to say that they'd rather the Empire not know about. The important thing is that it doesn't give them any clue that Karrde was harboring Luke Skywalker, who the Empire desperately wants to capture. Karrde later sends a message back using the same method, via the X-wing.
    • Winter tells Han about Ackbar's 'kids' acting up, and he inquires about the 'neighbors' — the New Republic politicians and the Empire, respectively. Problem is, this wasn't a code that they'd worked out beforehand — actually, they never worked it out at all. Winter came up with it on the fly because she knew they'd be listened in on, and just hoped Han would be able to work out enough of it to be useful. Han knows Winter means there's been some problems, but not just what they mean. This incident was, bizarrely, a case of Real Life Writes the Plot. Long before the book was released Timothy Zahn told some trusted friends about it and met them at a convention to discuss it further, only to realize that they were surrounded by scifi geeks who would know what he meant if he started talking about Luke and Leia and Han and Chewie, and then he'd be in trouble. So on the fly he called them Brother, Sister, Friend, and Copilot... and it worked.
  • In Robert Anton Wilson's Illuminatus!, a secret society places personal ads reading "In thanks to St. Jude for favors answered — A.W." as a code to their other members.
  • In KG 200 by J.D. Gilman and John Clive, a downed German pilot is hiding with a female spy who mentions that she gets her instructions via broadcasts from Loud Haw Haw, saying that lots of people listen to Radio Hamburg so she doesn't have to worry about being overheard. In response to the pilot's surprised look, she says it's not because the British people are about to rise up against Churchill, but for the laughs. The message she then gets tells her to get the pilot out of England—she doesn't mention that it also instructs her to kill him if it looks like he'll be captured.
  • In the Mary Russell mysteries, Holmes and Russell frequently use the "agony column" of the London Times to send messages to each other in a kind of code.
  • The protagonist of Mother Night by Kurt Vonnegut works as a radio propagandist for the Nazis in World War II, but he is actually a spy for the Allies. He's given a list of things they want him to find out about the Nazis, and after he finds them out he communicates the answer on his radio show by, say, coughing in the middle of a certain sentence if the answer is "yes" and not coughing if the answer is "no", or by using a certain word he wouldn't otherwise use, etc.
  • In the Prince Roger series personal ads on dating sites are used by several different groups to pass secret messages.
  • In Philip K. Dick's Radio Free Albemuth and its more polished rewrite VALIS, a subliminal message is sent to the public in the form of song lyrics so that the government won't intercept it but those who know the truth will be able to spread the message.
  • The Quest for Saint Aquin by Anthony Boucher is set in a future where Christianity is forbidden on pain of death. The protagonist is a priest traveling incognito, who makes contacts with fellow Christians via coded signs. For instance while stopped at a checkpoint he makes the sign of the cross while apparently searching for his papers. The guard in turn draws the symbol of a fish in the dirt, then scuffs it out and lets him through. Other tricks include having a rosary Hidden in Plain Sight as the buttons on the priest's coat.
  • In Red Dragon, Hannibal Lecter places a personal ad filled with Bible verse numbers in a tabloid as a coded message (the numbers refer to the nth letter on the xth page of his edition of The Joy of Cooking) to Francis Dolarhyde. The FBI decrypts it, and realizes that it told Dolarhyde where Will Graham lives; they send Dolarhyde another message to lure him into a trap, but he recognizes it for what it is.
  • In Replay, by Ken Grimwood, in one loop, Jeff and Pam use ads with various loop-derived future references to try to make contact with other replayers.
  • In A Running Duck (aka Fair Game) by Paula Gosling, the protagonists open a newspaper and are shocked to find an open death threat against them. The antagonist got the newspaper to print it by claiming it was an advertising gimmick that would be followed up in the next edition.
  • In Semper Mars by Ian Douglas, after UN troops take over the Heinlein Base and "relocate" all US Marines there to a tiny remote outpost, Major Mark Garroway sends a coded message to his daughter Kaitlin back on Earth, asking her to pass a message to "Uncle Walt". Since he knows the UN is likely to block any message with certain key words, he peppers the message with enough American and Marine-specific references to slip under the radar. The message is "Walt, you sorry-assed son of a bitch, listen up and listen good. The blue boys pulled a Pearl Harbor 1207 GMT 27 May. The boss is down, but okay. Forcibly relocated to Red Planet. Have capped guards and secured cat. Am marching on Derna, with complete openness." "Blue boys" refers to UN troops, who wear blue uniforms, "Pearl Harbor" refers to a sneak attack, "the boss is down" means Garroway is in command, "forcibly relocated" means "imprisoned", "Red Planet" is a reference to the Heinlein Base (Red Planet is a novel by Robert A. Heinlein), "have capped guards and secured cat" means that Garroway and his people have managed to escape, kill their guards, and obtain transportation. "Marching on Derna" is a reference to a key piece of USMC history - the Battle of Derna in 1805, which was preceded by a 600-mile march through the desert. This lets the brass know that Garroway and his people plan to make a similar trek across the Martian desert to secure the city of Mars Prime. While it's true that anyone with access to internet would eventually be able to figure out the message, the reason for wording it thus is to avoid automated filters in place by UN.
  • In A Series of Unfortunate Events VFD members communicate with "Sebald code", in which every eleventh word between two bell rings (or two mentions of bells ringing, if the communication is text-based) is the message. The character of Gustav Sebald, the Volunteer who developed the code, was a famous film director and sent messages with the code in his movies.
  • In Orson Scott Card's Shadow of the Hegemon Petra and Bean communicate by starting an e-mail signature meme: an image file of a dragon with a coded message in it and the words "Share this dragon / If you do / Lucky end for / Them and you", which reference the Dragon Army and Ender Wiggin.
  • Sherlock Holmes stories feature multiple examples. Conan Doyle seemed to like this one.
    • In "The Adventure of the Red Circle", someone places ads in the London Daily Gazette' "agony column" to send secret messages.
    • "The Adventure of the Bruce-Partington Plans" also features messages in an agony column as a clue, this time in the Daily Telegraph.
    • In "The Adventure of the Dancing Men", a series of dancing stick figures appeared in several locations visible to anyone who passed by. Holmes decides the figures represent letters and decodes the message.
  • Star Trek: In the DS9 novel "Warchild" Kai Opaka writes about a vision she had about a child uniting all the warring factions on Bajor after the Cardassians leave. She includes what Commander Sisko and Bajoran priests assume to be decorative calligraphy on the edges of the parchment. These turn out to be a message written in a very obscure Bajoran language where Opaka admits she hadn't received a vision but felt the situation on Bajor dire enough to invent a prophecy of a child uniting Bajor.
  • In Trial By Journal, Lily sends messages to the presumed dead Perry by calling him 'Hansel" (his character in a play) in the newspaper. In return, he calls her LAW, and sends replies via the painting everyone thinks a gorilla is making. It Makes Sense in Context.
  • Watership Down. Bigwig has drawn unwelcome attention by talking to the seagull Kehaar to arrange a breakout of does from the dictatorship warren of Efrafa, and he's forced to delay the breakout when General Woundwort turns up to interrogate him. To convey the change of plan to Kehaar (that the breakout will be tonight), he disguises his message as a spell to drive off the bird ("Fly away great bird so white, and don't come back until tonight") and even convinces one of the other officers to join him in saying it. The officer is dubious as to the spell's effectiveness, but sure enough the bird flies off (and returns just in time that night to save Bigwig).

    Live-Action TV 
  • Andromeda: In one episode, the ship receives a message from Dylan to arrive in a certain system. Tyr says that with Dylan's behavior and constant blinking, it's obvious he's not telling something. Rommie replies that he is telling something — the number of blinks can be deciphered as a code for a military protocol ordering them to arrive prepared to fire at the ship holding him.
  • Batman (1966): In one episode, Batman talks to one of the villains over a broadcast radio station, but requests that all other citizens of Gotham switch off to avoid hearing his private message. Naturally they oblige.
  • Burn Notice: Michael Weston has been known to create or receive coded messages in public locations. One earlier example showed him writing a cryptic note to another spy on the sidewalk in chalk.
  • Chuck:
    • Steven Bartowski provides Ellie Bartowski with a method for contacting him through coded messages in the personal ads.
    • Chuck also takes the microphone at Sarah's high school reunion, puts a spotlight on a couple of people in the audience and starts reminiscing about high school with them. Neither Chuck nor those men attended Sarah's high school; he was just identifying criminals for Sarah and Casey, who he didn't have time to approach personally.
  • Colonel March of Scotland Yard: In "Death in the Dressing Room", a Javanese dancer incorporates movements meaning "Help. Danger" into her dance. Fortunately for her, Colonel March understands the meaning of Javanese dance moves.
  • Dexter: In the first season, the Ice Truck Killer leaves little clues in his kills that makes it very clear to Dexter that he's speaking to him personally and not the police.
  • Doctor Who:
    • "The Power of the Daleks": The rebels place a secret message detailing the time and place of their next meeting hidden in a notice placed on a public noticeboard.
    • "Bad Wolf" was a subtle message sent all through time and space by Rose, which she sends to send her past self to rescue the Doctor.
    • "Blink": The Doctor records a message that Billy Shipton adds as an Easter Egg on some very specific DVDs (corresponding to the entire DVD collection of Sally Sparrow) decades later. It makes no sense whatsoever, until late in the episode where it's revealed to be The Tape Knew You Would Say That: Sally's reactions to the scene form a perfectly cohesive conversation with the Doctor (who has a transcript of her reactions) regarding the TARDIS and the Weeping Angels.
  • Endeavour: In "Pilot", a university professor and cryptic crossword compiler uses his weekly crossword to supply his paramour with the time and location of their next assignation.
  • The Equalizer. In "The Distant Fire", McCall finds a postcard pinned to a noticeboard at a bar he frequents. He scribbles out parts of the writing on the back to reveal a message hidden there by an old adversary.
  • Father Brown: In "The Two Deaths of Hercule Flambeau", Father Brown sends a desperate message to Flambeau by placing an extremely cryptic advertisement in the newspaper's classifieds.
  • In the 2000 remake of The Fugitive, Richard Kimble communicates with people aiding him via personal ads in the newspaper. Unfortunately, in one episode, Gerard finds out and sets a trap for him.
  • Get Smart: In one episode, the Chief (disguised as a singing waiter) communicates a message to Max and 99 by slipping code phrases into the song he is singing.
  • The Hour: Freddie discovers that a secret code that is being spread through crossword puzzles in the newspaper, though you need a special key to find it.
  • iCarly: In "iPsycho", Carly and the gang have been kidnapped by Nora and need to get a help message out so someone can rescue them. She's watching their every move, so they ask if they can send a birthday video to their friend Gibby. She agrees to let them do so, and they open it with a bit about celebrating Gibby's birthday "every Fourth", followed by Freddie saying "word!". Though initially confused by the video (not the least of which being because it isn't even his birthday), him and his brother quickly realize that this was the three of them telling Gibby to put together every fourth word they say in the video to get the real message.
  • JAG: In "The Black Jet", Jack Keeter has downed in Iran with secret airplane and is detained by the authorities. When first meeting Harm and Mac, accompanied by an Iranian official in prison, he says "No Martin Baker" several times over. Harm later decodes the message: Martin Baker is the manufacturer of ejection seats, and thus Keeter didn't eject but landed the plane and was captured elsewhere.
  • In "The Wedding Job" episode of Leverage, the sermon Nate delivers at the wedding (while posing as a priest), is clearly intended to be a message to Sofie, who is in the crowd, about their relationship.
  • In the German series Löwengrube, the religious (and somewhat naïve) mother-in-law of the protagonist mentions one day that the people who beg at her door were so pious nowadays. Since he works for the criminal police, he remembers what he recently learned about hobo signs — and indeed, there is one at her door, meaning "act as if you were pious".
  • Lucifer (2016): In "Expire Erect", there is a hostage situation at Lux, a nightclub owned by the titular Lucifer. While he is incapacitated by an injury, the hostage taker gets his food delivered, but it is the wrong sandwich. Detective Dan Espinoza, who is lead outside, didn't make a mistake, but is using the sandwich to send a warning to Detective Chloe, one of the other hostages. The sandwich is a southwestern-style from a restaurant called Luis. Dan's message to Chloe is that SWAT will breach the room from the southwestern corner of the room.
  • Million Yen Women: Telling all the rest of the household what she knew about the invitation sender, some time after the fact, turns out to have been Minami's way of telling the invitation sender that she had figured out their plans and identity.
  • Murder, She Wrote: In "The Dead File", a cartoonist hides blackmail threats in a daily comic strip.
  • Murdoch Mysteries:
    • In "A Study in Sherlock", David Kingsley (a.k.a. Sherlock Holmes) insists Moriarty communicates with his gang via coded obituaries in the local paper. Murdoch and Brackenreid are dubious, but as which much else in the case, the young Sherlock proves to be correct.
    • In "The Artful Detective", Brackenreid notices an extra race published in the racing form; he's familiar with the track and draws Murdoch's attention to the discrepancy. The team compares the horse names to the profiles of several recent murder victims and finds several of the "horse" names are each descriptive of their victims. They come up with the hypothesis that the victims and a few other people are actually killing each other in a Deadly Game, and they stake out the racing form's publisher. Sure enough, the "horses" they have matched to their corpses are missing from the next "running" of that non-existent race, but a new entry is added: "Artful Detective". Guess who soon finds himself attacked in the street?
  • Oliver's Travels: Oliver's friend who writes crosswords under the name of "Aristotle" goes missing after getting on the wrong side of a conspiracy, but Aristotle's crosswords continue to be published, and at one point Oliver realizes that the most recent one contains a hidden message indicating who's behind the conspiracy.
  • Person of Interest.
    • Privacy terrorist group Vigilance communicates between its various cells via this method, as they're Properly Paranoid about government surveillance (methods include a message written on a wall in infrared paint, and a code embedded in a spam advertisement).
    • In Season 4, the Machine does this to communicate with Team Machine without Samaritan (which now monitors all CCTV cameras and phones) finding out.
      Finch: When you said your communication with the Machine was limited, you didn't say that it wasn't talking to you at all.
      Root: If she talks, Samaritan would see. I get whispers. New cover identities hidden in the static of a phone, a map and a message encrypted in an infomercial. She was supposed to remake the world. Now, God's on the run.
    • In "YHWH", John Reese is being held captive by the Brotherhood, so the Machine sends a fax message to the room he's in, to the puzzlement of the guards.
      Floyd: It's an old fax machine.
      Dominic: What does it say?
      Floyd: (reading) Sharp right leg. Left knee, ACL. Tactical blade. Glass jaw.
      (Reese kicks mook's knee, then headbutts him in the jaw, grabbing the tactical blade off him to cut his zipties)
    • The Machine does the same thing in an earlier episode when Root is the one being held captive, using Morse code transmitted at a frequency that Root will hear but her captor will not, because they're older and so their hearing isn't as good.
    • In Season 5, it's revealed that Samaritan is communicating with its operatives via Fake Static in radio transmissions, forming an encrypted morse code.
  • The Professionals. In "First Night", an Israeli government official is kidnapped and forced to read out a taped ransom demand. He inserts pauses after a certain number of words in a pre-arranged code to convey information about his kidnappers.
  • The Pretender: Argus asks for Jarod's help in this way by placing an ad in the newspaper.
  • Rubicon: A secret society publishes messages encrypted in crossword puzzles in newspapers.
  • Star Trek: The Original Series: In "Bread and Circuses", Kirk calls up to the ship just as the enemy's guards threaten him with guns, so instead of telling Scotty to beam down a security detail, he says "Condition Green." Although that sounds like it means "all is well", it's a duress code meaning "We're in trouble, but take no action at this time."
  • Sue Thomas: F.B.Eye: Used by terrorists in "The Lawyer". A terrorist in jail sends a message to his organization to change their plans for an attack by having his lawyer read a statement on the news about how sad he is to miss his nephew's birthday party. The FBI team brings in a special expert on these types of hidden-in-plain-sight messages to help decode the communications.
  • Supernatural: Sam and Dean have developed "Hunter's Lingo", which are phrases they can work into conversation to let them know the other is in trouble. "Funkytown" means "Someone currently has a gun on me", "Something stuck to my shoe" means "I'm being followed," and "Poughkeepsie" means "Drop everything and run."
  • Survivor U.S. Season 41 contains an immunity idol with a twist feature. A shared immunity is hidden each camp of three tribes formed at the beginning of the season. Anyone who finds it first sees a message warning that it comes with a large risk and they can choose to either put it back or open it up and keep reading. If they choose to keep reading, they learn that they have lost their vote at Tribal Council until someone at each of the other camps has found the idols at those camps. Furthermore, in order to activate the idol and both gain the immunity and get their vote back, they must say a secret phrase during the immunity challenges. If the other two secret phrases are also said within the same challenge, then they're golden. The secret phrases are as follows: "I truly believe that butterflies are just dead relatives saying hi," "I'm as confused as a goat on AstroTurf" and "I didn't realize this until now... broccoli is just a bunch of small trees."
  • Time Trax: Lambert would send messages to the future by placing coded personal ads in the newspaper.
  • Timeless: Jiya, stranded in San Francisco in the 1880's, sends a secret message to the present by having herself photographed; her message is in Klingon script disguised as designs on the blanket she is sitting on.
  • In Through the Dragon's Eye, Jenny manages to pass on a warning to her travelling allies that the evil Charn has returned to Pelemar by having her ally Morris knit her a scarf with "HELP! CHARN!" as a 'pattern'; as Charn, like all natives of Pelemar, can't read, he was unaware that she had passed on the message to his old adversary Gorwen.
  • The Wild Wild West: James West communicates with his partner, Artemus Gordon, through the use of coded symbols written on a menu in one episode and via Morse code punched into a newspaper in another.

  • Many rock bands have been accused by Moral Guardians of putting hidden messages in their album covers or the lyrics of their songs, some of which would only be deciphered if you played the records backwards. The Beatles are the most famous example. Though sometimes these hidden messages were clearly intended by the artists themselves, others were nothing more than extremely far-fetched fan theories. One of the most extreme cases involved the metal band Judas Priest, who were sued in 1990 for allegedly placing a backwards message that caused the suicides of two teenage boys in 1985. Singer Rob Halford infamously responded by saying it would be more productive for the band to put subliminal message urging the fans to "buy more of our records".
  • Blake Neely's score album for the first season of Riverdale spells a message with the first letter of each track: RIVERDALEISANORDINARYTOWN
  • Frank Zappa included secret messages and clues in the album art work and lyrics of his songs that are still being decyphered by fans and music historians worldwide. He also had at least one secret word in each concert that he gave, usually inside jokes between him and his band members.
  • Edward Elgar's orchestral piece "Enigma Variations" gets its name from the composer's hint that the work supposedly contains a musical cypher of "a counterpoint on some well-known melody which is never heard." What exactly the secret melody might be has never been conclusively solved.

    Tabletop Games 
  • Dungeons & Dragons:
    • 3E had a skill called "Innuendo" for this exact purpose. It was removed in 3.5E (folding it into the "Bluff" skill), presumably, because it was too specific to be worth spending skill points on.
    • There's Thieve's Cant, a language known only to Rogues that utilizes both a mix of obscure (and rather inefficient) slang and jargon to hide information in seemingly-normal conversation and a system of symbols and signs, used mostly to mark gang territory and dangerous areas.
    • Druids have a secret common tongue called, appropriately enough, Druidic. A message left in Druidic is automatically spotted by fellow druids, while non-druids need to pass a Wisdom check to see it in the first place and need to use magic to understand it.
  • The staff at Steve Jackson Games were not allowed to release the title of one game supplement in the Power-Ups series, and the forum speculation was that they were trying to create a sudden burst of interest on release to fuel impulse buys. The author even said, "I've been told that the secrecy around Power-Ups 5 does, indeed, have something to do with impulse buys." An entire game's fanbase facepalmed at the release of Power-Ups 5: Impulse Buys.

    Video Games 
  • In Back to the Future: The Game, the franchise's tendency toward I'm Mr. [Future Pop Culture Reference] pays off, resulting in an accidental version of this trope, when Marty discovers that one "Carl Sagan" was gunned down by gangsters in 1931, which flags Marty's attention enough to dig deeper and discover that "Carl Sagan" was, indeed, Doc.
  • City of Heroes has villains getting bank robbery missions in such a manner, by looking in the newspaper for encoded messages from their Brokers.
  • The Illuminati in Deus Ex use this interestingly. They communicate primarily by heavily encrypted e-mails, which they know their opponents will pick up and read. However, the information isn't in the e-mail, it's in the encryption key. Each key means "Meet me at place X, at Y o'clock, on day Z".
  • In the Bad Boys Love route of Hatoful Boyfriend, Nageki tells his "brother" Hitori that he's fine when he's clearly in pain due to his illness, causing Hitori to ban him from using the phrase "I'm fine" around him. Nageki only ever uses it again years later in a letter to Hitori from St. Pigeonation's, to let him know that something is very wrong.
  • In Iji, Dan communicates with Iji by speaking, in English, through every speaker in the complex. Since the aliens never bothered to learn any human languages, they can't understand him, and since he uses every speaker, they can't use the active speakers to track Iji.
  • In The Phantom of Venice, one of the Nancy Drew computer games, the members of the mysterious crime ring that's responsible for the thefts of priceless art and relics use these to communicate with each other. Methods include the arrangements of particular flavors of chocolate inside a gift box, chess games that actually translate to addresses when the board is read as a letter grid, and tying tiny notes to the legs of the pigeons in the squares around the city.
  • Pokémon:
    • Used as a teaser in Pokémon GO. One of the announcements is accompanied by a five-sentence paragraph. The first letter of each sentence spells out U-N-O-V-A, the setting for Pokémon Black and White, strongly suggesting that Generation V Pokémon would be coming to Pokémon GO in the near future.
    • Used in another teaser involving a throwback to Unova, this time for Pokémon Legends: Arceus: "Rare footage of the Hisui region discovered!" is a severely deteriorated video in which the cameraman is discovered and attacked by a Pokémon, but the video had degraded too far to see what it was. At one point, he notes the time as "7:06, no, 7:07." The Pokémon filling up entries #76 and #77 in the Unova Pokédex in Pokémon Black and White happen to be Zorua and Zoroark, a hint that the next Pokémon to be shown would be Hisuian Zorua and Hisuian Zoroark.
  • In Resident Evil 2 (Remake), a letter from Chris to the rest of S.T.A.R.S could be found and it appears to be a casual letter to his co-workers about his vacation in Europe. But if one reads between the lines, the letter actually details Chris's progress on his investigation of the Umbrella Corporation and telling his comrades to stay safe. In the original game however, Chris's planned investigation was clearly written in his diary.
  • Space Quest III: The Pirates of Pestulon has Roger discovering a secret decoded message from the Two Guys from Andromeda calling for help while playing the arcade cabinet game "Astro Chicken".

    Visual Novels 

  • Clockwork: Before leaving for Arcadia under heavy coercion, Cog leaves a letter for his best friend Boris. It appears to be just a friendly effort to ease Boris' objections to his decision, but the first letters of each line spell out "HELP ME".
  • Girl Genius: Here, a bunch of Jagers are posing and Chewing the Scenery, probably loud enough to hear for not only a few panicked bystanders, but half of the town. Dimo's first phrase, however, had a very specific meaning,note  which the only intended listener recognized immediately (and was somewhat shocked). And it's something they say openly only when they are sure no outsider can possibly overhear.
  • Sleepless Domain: In various strips there is blocky secret code hidden amongst the often wildly geometric cityscapes.

    Web Original 
  • LISDEAD is seemingly an inversion; it's encrypted and secret to nobody except for a certain mysterious "Him".
  • Joked about in Rocked. While reviewing Metallica's album St. Anger, he theorizes that there must be a hidden message to the album due to its harshness and distinct departure from Metallica's usual sound. The final track on the album (kinda) proves him right when James Hetfield repeatedly shouts the word "KILL" as loud as possible. This scene is accompanied by Luke seeming hypnotized and picking up a box cutter briefly before putting it down.

    Western Animation 
  • On Ben 10: Omniverse, Kevin goes missing to rescue the Plumbers' Helpers from the Rooters. He leaves Gwen with what seems to be a love poem with many grammatical spelling errors. However, Gwen deciphers it with a magic decoding spell and it is revealed to be a message telling her Ben and Rook to go after Manny and Helen while he is rescuing Alan.
  • Parodied in The Flintstones theatrical film The Man Called Flintstone: Fred, who has to stand in for an injured spy, is told to find a fellow spy, who will respond to the code phrase "Fifty flying firefighters" with "Bubla." Fred, not really sure how he's supposed to do this covertly and with no clue what this spy looks like, just wanders around saying "Fifty flying firefighters" to everyone he meets whom he doesn't personally know, which only creates strange looks in his direction. When Fred meets a lady who looks sufficiently spy-like and she doesn't respond with the intended phrase (because she isn't a spy), he outright tells her in frustration, "You're supposed to say 'Bubla'!" Fred DOES eventually find the spy, but by then, he's too frustrated to say "Fifty flying firefighters" to anyone anymore, and the spy has to coax that phrase out of Fred.
  • In one episode of Foster's Home for Imaginary Friends, Bloo becomes famous for starring in a deodorant commercial, but discovers that his "contract" is actually adoption paperwork, allowing his agent to act as his abusive parent and prevent him from contacting anyone who could help him... except, Bloo realizes, through his various acts on TV. He then proceeds to sing several musical numbers about how he's being held against his will, and finishes with tap-dancing "HELP ME" in Morse Code. It works, eventually.
  • In one episode of Gargoyles, after Goliath, Hudson, and Bronx are captured by The Pack, the younger Gargoyles discover a commercial on their TV, in which a woman who is clearly Fox stresses the names of Brooklyn, Broadway, and Lexington (Avenue) while encouraging the viewer to use the subway, cluing the three in to where the Pack is holed up.
  • Crops up in an episode of Gerry Anderson's New Captain Scarlet when Captain Ochre is captured by Mysteron Agents and forced to check in with headquarters at gunpoint. She uses a pre-arranged duress code-phrase to alert Spectrum that she's in trouble, and Captains Blue and Scarlet are dispatched in a Rhino APC to rescue her. Unfortunately, the Mysterons are a lot smarter in the remake, and not only did they see it coming, they were counting on it so they could jack the Rhino and blow up a nuclear power station with it.
  • In the second season of The Secret Saturdays, Argost starts sending Zak secret messages regarding cryptids as part of television show Weird World.
  • The Simpsons:
    • In "My Mother the Carjacker", Mona Simpson encodes secret messages to her son in the newspaper, in food articles, using the first letter from each word.
    • Homer sent a message to Lisa in the New York Times Crossword Puzzle. Defictionalized by the NY Times running that same puzzle.
    • Paul McCartney, in-universe, would hide recipes inside of his songs, which can be heard by playing the song backwards. This is made up for the show, but the end credits for that episode would actually have McCartney reading out a soup recipe played backwards and quietly over the music.
  • Voltron: Legendary Defender: Matt leaves one to Pidge and his father by listing the wrong birthday on his gravestone when he fakes his own death, giving them the coordinates of his actual location.

    Real Life 
  • Before the advent of other means of private communication, many people would place encrypted (using simple substitution ciphers) adverts to lovers in newspapers. Some mathematicians (such as Charles Babbage) were known to keep their minds sharp by breaking them (and in at least one case place similarly encrypted advice not to elope).
  • Hobos left marks called "Hobo Signs" on people's fences telling other hobos about the nature of those living there.
  • During World War II, the Allies would send messages to friendly resistance fighters, spies and other clandestine groups behind Axis lines by making announcements over civilian BBC broadcasts. While the broadcasts were open and able to be listened to by the Axis, the messages themselves would be meaningless phrases whose meaning would only be understood by the intended receiver.
    • Although, as the example of the first two lines of a Verlaine poem broadcast shown in the movie The Longest Day broadcast separately on two separate days before June 6, 1944, demonstrates, someone in the Abwehr did correctly guess the import of such messages (in this case: "the landing in France is imminent").
    • The use of phrases and code names even in both clear and encrypted communication also falls into this territory, for instance the Japanese high command sent the message "Climb Mount Niitaka" to Admiral Nagumo to launch the attack on Pearl Harbor.
    • An odd-looking advert for the dice game "Deadly Double" had gotten the FBI suspicious, as it had all the trappings of a Public Secret Message announcing the Pearl Harbor attack. It was apparently just a coincidence, though.
    • A series of newspaper crossword puzzles in 'The Daily Telegraph'' almost spoiled D-Day (known as the Crossword Panic of 1944), as each of them would contain words the militaries were using as code for their operations, such as "Utah," "Dieppe," "Juno," and "Neptune." It was soon discovered that this was a massive coincidence, however, and the author of these crossword puzzles had no idea they were in use by the Allied forces. The truth was eventually revealed: The author was a school headmaster who encouraged his students to find interesting words to put into his crosswords. Some of his students lived near a military base and would spend their free time listening to the soldiers, of whom they were getting those "interesting words" from.
  • Some US units used "code talkers" — radio operatives who would translate their messages from English into a language that was unknown to Axis forces (typically a Native American language, for some of which, including Navajo, there were no published textbooks or dictionaries). As the absence of messages might have clued off the allies, code talkers were encouraged to just have "private chatter" on days with less communication to take care of. Similarly, terms that would usually be loanwords in Navajo as well as proper names were rendered as calques or complicated cirucmlocutions - it helps that Navajo grammar both enables this and makes it frustratingly hard to understand to non-native speakers. For example, the code word for submarine was "iron fish".
  • Numbers Stations are clearly sending some sort of coded message, but it's meaningless to anyone but the intended audience.
  • One of the features of "public key encryption" is that you can publish one key, letting anyone send you a message that no one without the other key can decipher. Or conversely, you can encrypt with the private key so that everyone can read your messages knowing they could only have come from you. And you can do both at the same time.
  • Gene Roddenberry had served in World War II with a man named Kim Noonien Singh. They lost touch after the war. Roddenberry named two characters after Singh, hoping to attract his attention — Khan Noonien Singh in the "Space Seed" episode of Star Trek: The Original Series (and Star Trek II); and Noonian Soong, Data's creator in Star Trek: The Next Generation.
  • A fairly common (and easy) method of sending secret messages in the past was to write an innocuous letter then write between the lines using a clear fruit juice, such as lemon or apple. The recipient would need to know that there was a message and by heating the paper, the fruit-juice words would be "cooked" and become brown and thus visible. This is believed by many to be the origin of the saying "to read between the lines".
  • One unusual National Weather Service forecast from 2013 contains an Open Secret. In one section, the first letters of each line spell P-L-E-A-S-E-P-A-Y-U-S, please pay us. Because of a US government shutdown, the employees who prepared the message were working without pay. News organizations exposed the secret, but only after the NWS had sent the message.
  • In The '90s, a blackmailer in Germany became somewhat famous. Since one of the messages in the newspaper had the text "Dagobert [Uncle Scrooge's name in Germany] greets his nephews", the press nicknamed him "Dagobert" after this.
  • Viktor Suvorov mentions that during his work, he was supposed to leave a message for an agent by sticking a drawing-pin into a pole. Unfortunately, there were so many pins already that they had to devise a separate system — he or his wife went to a park and marked certain letters on a certain plaque with lipstick.
  • A "duress code" is a covert signal to call for help without the knowledge of the persons threatening you. For instance, home alarms often have two shutoff codes: the real one, and the one you enter if a robber is forcing you to. That's the code that silently alerts the police.
    • In World War II, if an agent wanted to visit a safe-house, he'd simply call the agent at the safe-house and ask if it was genuinely safe to visit. If it was safe, the answer would be "no", but the duress answer would be "yes." (If you're surrounded by gun-wielding Nazis, which would you rather they hear you say?)
    • One that has been suggested for girls in western countries who are risk of being taken by their parents to another country and forced into an Arranged Marriage is to slip something metal (like a piece of cutlery) into their pocket so that they set off the metal detector at the airport and can ask security for help.
    • Some establishments will offer this to their female patrons in the form of an "Angel Shot", or any other made-up entry on a menu that solely exists as a way to give women that found themselves on a bad date, a way to discretely alert a waiter or bartender that they are in need of assistance.
    • This soldier infamously crossed his fingers while shaking hands with Hillary Clinton, which is the signal for "I am doing this under duress"note .
  • After his plane was shot down over Vietnam, US Navy pilot Jeremiah Denton was taken prisoner by the Viet Cong, who later put on a televised press conference to show how well they were treating enemy captives. Denton repeatedly signaled the word 'TORTURE' in Morse Code by blinking his eyes.
  • When John McCain was shot down and captured by the North Vietnamese and forced under torture to give a confession of war crimes, he used terminology that would sound ridiculous to a native English speaker (like calling himself an "air pirate") to signify he was not cooperating willingly.
  • Similar to the above, when the crew of the USS Pueblo was captured by North Korea in international waters during The Korean War, the Koreans distributed a picture of the crew to show that they were well cared for during their stay. Looking closely, several crew members appear to disagree. When pressed about the gesture, the crew called it the "Hawaiian Good Luck Sign". When the commander was forced into confessing to spying, he concluded with this: "We paean the great state of North Korea and its leader." "Paean" is a real word, so the North Koreans were able to look it up and confirm its meaning, but it's pronounced very similarly to "pee on", which the North Koreans didn't catch.
  • One method of contacting 911 regarding domestic abuse or violence is to call the number and pretend to be ordering a pizza, as depicted in this commercial, with the audio taken from a real 911 call. A woman calls 911, gives her address, and remarks that she wants to place an order for pizza; the dispatcher asks if she really has an emergency, and she responds "Yes." The dispatcher, catching on, asks if there's anyone else in the room listening in, which she confirms. She's then able to answer some yes-no questions about her situation for the dispatcher, who sends help.
  • As mentioned in Bravo Two Zero, people in the military, particularly special forces who may be likely to be captured, will often agree on a sign that they are being forced to do something under duress. In this book, one of the captured soldiers is forced to make a video message stating that all's well. He is given a cigarette to add to the illusion. His signal that all's not well is to hold the cigarette differently than he usually would.
  • One urban legend describes a prisoner of war forced to write a letter to his family saying that he is being treated well. In the letter is a cryptic sentence: "Please give little Jimmie the stamp for his collection." The family doesn't know anyone named Jimmie, so they realize that it must be a clue. They steam the stamp off the envelope, and on the other side is written the truth of the prisoner's condition: "They've cut off my [hands/legs/tongue]."
  • Arrested by the Nazis during World War II for suspicion of hiding Jews in her house, Corrie ten Boom received a letter from her sister with bad news (their father's death). She then noticed the address was written in a hand that sloped uncharacteristically forwards, pointing to the stamp. The stamp had the message "All the watches in your closet are safe", letting her know the hidden Jews had not been found by the Nazis.

    Using "watches" as a codeword for Jews was fairly common in the Dutch resistance. "We have a woman's watch here that needs repairing. But I can't find a mainspring. Do you know who might have one?" was one way of saying that there was a woman in need of a hiding place, but none available. Any references to issues with a watch's face meant a Jew whose features were especially Semitic — "Do you know someone willing to take on the extra risk?" And "This watch cannot be repaired — do you have a receipt?" meant "Someone has died. We need a burial permit."
  • The Special Operations Executive (SOE), which sent many agents into occupied countries during World War II, provided them with duress codes and other security checks that would blend in with the normal textnote . However, when the Gestapo forced captured "pianists" (wireless operators) to send false messages or attempted to use captured equipment themselves SOE headquarters would infamously ignore their own security protocol and keep trusting the communicationsnote . On one occasion, the British contact in England told the agent attempting to sound the alarm that they made a mistake: "That's the duress code, you need to remember not to use that." Needless to say, things went downhill from there, with many agents being delivered directly into the hands of the Gestapo after the SOE had arranged drops with a captured agent or an enemy operator on the other end.
  • If the pilot of an aircraft sets their transponder code to 7500 or says "squawk 7500" over the radio and then does not respond, air traffic control will assume the aircraft is being or has been hijacked. There are also other, confidential, measures taken. In fact, great emphasis is placed on the part of radio training where pilots are instructed how to avoid accidentally flipping their transponder to 7500 while switching codes.

    Other transponder distress codes include 7600, which translates roughly as "My radio is not working properly"note , so the Air Traffic Controllers will know why you don't respond to them on the radio, and 7700, which is a general-purpose Distress Call.
  • From a letter by a Jewish family which passed through Nazi censorship:
    "Dear XXX, let me assure you, all the stories about Jews having to suffer in Germany are nothing but propaganda. We are fine in every way, we are not harassed by the government, and we wouldn't wish to be anywhere else, except maybe with our dear aunt Sara — Sichrona la olam!" (The latter being a Hebrew phrase roughly equivalent to "May she rest in peace".)
  • Military personnel on guard or patrol duty will typically have a "distress call-sign" which they use in place of their own to discreetly call for help.note  Another common tactic is to have a very specific but seemingly innocuous statement (Such as "Is Frank still dating Lisa?") which, when said, will alert their allies that something is wrong.
  • In World War II, when the Japanese let captured American soldiers speak on the radio to assure the troops they were being well-treated, they often said things such as they were allowed to keep their clothing — that is, they were still dressed in whatever rags their clothes were after battle and POW camp. This were improvised, but still conveyed enough to the Americans that they were not being treated well.
  • At the National P.O.W. Museum (496 Cemetery Rd, Andersonville, GA), by the Andersonville civil war prison, there are a number of video screens to watch, including one screen showing black and white footage from World War II Japan. In this video there is a prisoner leaning on a railing, facing generally toward the camera. The man is unobtrusively giving the Hawaiian good luck symbol, so this gesture in film pre-dates The Korean War. Museum staff were unaware of this.
  • In 2010, the Colombian army needed to tell soldiers captured by the FARC to keep up hope and prepare for escape (while the army prepared to raid the FARC compounds) without letting the FARC know what was coming. They wrote a pop song containing a hidden message in Morse code and played it on the same radio stations that relayed family messages for the captives.
  • With the rise of video-telecommunications because of the COVID-19 Pandemic and people being isolated at their homes with potential abusers, the Canadian Women's Foundation developed a simple hand signal to alert other people on those video calls the person in distress. One simply has the palm face the camera with the thumb over the palm, then the person covers the palm with their fingers. It has been used outside of such calls to call for help. In early November 2021, a 16-year old kidnapping victim was in the car with her kidnapper and signaled to another car with this hand signal. The driver recognized it and called the authorities, saving the young girl's life.