In a particular setting something is out of place. A very distinctive something, something that could only have gotten there if someone in particular had been there. For whatever reason, that person came here and did... something. Then, before they left, for some reason, they left the object in question.
The types of objects that are left are too many to mention, but they must be distinctive enough to be recognized when they are found. Sometimes they are blatantly obvious, and other times they are the kinds of things that only a Great Detective would notice.
Regardless, the implication is that the owner of the object was here, and the object is the proof!
If it's not a plant, then spotting the item could be followed directly by the owner walking in. It could be a hint that the owner is actually in the room, hiding in the closet. Or the item could be covered with dust, indicating that it has been sitting there for a long time.
A variation has the significant item showing up with another person, rather than in a particular place. For example, if you thought Alice and Bob didn't know each other, but then you see Bob carrying Alice's cigarette lighter, you might start to wonder.
Although this trope can appear in many contexts, it is a particular staple of detective fiction. This may sometimes bump against Conviction by Counterfactual Clue, if it clinches a case in-story, but the reader is able to figure out other explanations that would establish reasonable doubt.
- Discussed in a filler-arc of Higurashi: When They Cry when Rena's Nice Hat is found covered in blood just after the the town is killed (supposedly) by natural gasses from the swamp, it is suggested that she purposely threw it into the river to be found, as a clue that there was foul play afoot. The accompanying flashback showing Rena being murdered by several knife-wielding men confirms that this is indeed the case.
- In the 2006 anime adaptation of Fate/stay night, Archer's true identity is never explicitly revealed, but when he dies, as his corpse Disappears into Light, Rin's necklace is left behind. At the beginning of the story, Rin gave her necklace to Shirou for protection, so the implication is that Archer is Shirou from the future.
- Kimagure Orange Road has a strange case: before the series, Madoka had a red straw hat she'd always wear, but gave it to Kyosuke when he arrived in town as she started having feelings for him, without telling her Only Friend Hikaru what she had done with it or Kyosuke telling his family where he got the hat he treasured. Shortly before the end, Hikaru, who also has fallen for Kyosuke, happens to mention it Kyosuke's sister Manami, who promptly goes and grabs it in Kyosuke's room for Hikaru to recognize-and thus realize her best friend and the boy she liked were in love.
- Robin Series: In order to frame Tim for Batgirl's murder a corpse was dressed as Batgirl and left with one of his signature R shaped batarangs jammed in it. For extra points he was lead there to be found by the cops just as he discovered the body.
- In An American Tail, Bridget and Tony are looking for Fievel, who got lost during the fire at the pier. Papa Mousekewitz, who had given up his son for dead, refuses to believe that it's the same Fievel Mousekewitz, until he is presented with the hat he himself gave Fievel earlier in the film.
- Tangled: Toward the end, Flynn spots one of Vladimir's ceramic unicorns, letting him know help out of his current situation is at hand. The ruffians from the Snuggly Duckling are nearby, ready to become Big Damn Heroes.
- Blade Runner. Officer Gaff likes to create little figurines and leave them behind. At the end of the movie, Deckard finds a unicorn left by Gaff outside his apartment (in which Rachel was hiding). This showed that Gaff had been there and didn't capture or kill Rachel or notify the other police of her presence the way he should have.
- Canyon Passage: After Mac is murdered, his trademark lucky gold nugget is found in George's possession. Combined with Hi having seen him steal gold dust from the company safe, this makes a pretty airtight case against him.
- In Circus of Horrors, Evelyn realizes that Dr. Schüler is really Dr. Rossiter when she sees him wearing the distinctive ring that Dr. Rossiter always wore.
- Clear and Present Danger
- Felix Cortez first becomes suspicious that the series of attacks on the Medellin Cartel aren't just guerrillas or a rival cartel after finding a stray shell casing from one of the US Special Forces' team's M16s at one of the attack sites.
- Later on, while investigating an alleged car bombing at a cartel leader's villa, the presence of an exotic explosivenote in conjunction with a cellulose residue leads Cortez, and separately Jack Ryan, to conclude the "car bomb" was actually a special laser guided bomb dropped by an American aircraft.
Cortez: The Americans are here...
- Deewaar: When Vijay finds Anita dying, he spots one of Samant's signature cigars on the floor and correctly deduces that they were responsible.
- In The Freakmaker, Burns makes the mistake of wearing the medallion he took off Bridget when he and Lynch abducted her, which attracts the attention of her classmates when the visit the freak show.
- Narrowly averted in Frenzy. A murder victim grabs the murderer's distinctive cross pin at the last minute. The murderer notices only after dumping the body. He retrieves the pin before anyone else can find it, but the trouble he has in retrieving it creates new, albeit less definite, evidence.
- Hangmen Also Die!:
- Czaka's distinctive lighter, with his initials engraved, is used as part of the frame-up against him.
- Inspector Gruber's tendency to leave lots of empty bottles around after drinking is also used as part of the frame-up against Czaka.
- In Inglourious Basterds, the shoe and autographed napkin left behind by Bridget von Hammersmark when fleeing a bar where several of the Basterds were involved in a fatal shootout with a German officer let Colonel Landa know she was present, when he investigated the scene. The shoe is brought up again later, to von Hammersmark's dismay.
- At the end of Miracle on 34th Street, Kris's cane is seen inside the house that Susan insists is her Christmas present, convincing Fred that Kris really is Santa Claus.
- In the movie Life, Eddie Murphy's character sees his father's heirloom pocket watch — the one he lost to the card sharp he was convicted of murdering — in the possession of the deputy who arrested him for the murder, and puts two and two together.
- Missile X: The Neutron Bomb Incident: The hero frisks a knocked-out henchman and finds a gaming chip from the Baron's casino. Guess where he goes next?
- In My Darling Clementine, James Earp shows off a distinctive cross necklace shortly before being murdered; much later, Doc Holliday's girlfriend is seen wearing it, making Wyatt think Holliday was responsible for James's death. (She was actually trysting with one of the real culprits.)
- Invoked by Abigail in the second National Treasure when she deliberately drops one of her earrings in the Oval Office, then uses that as a distraction for Ben to examine the President's desk, on the grounds that it wouldn't do for an earring belonging to her to be found there.
- A verbal example in None Shall Escape. Marja figures out that it was Wilhelm that raped Anna when Anna mentions the rapist's cane.
- In Rancho Notorious, Vern sees Altar wearing the one-of-a-kind brooch that he gave to Beth on the day that she was murdered, and knows that one of the outlaws in Chuck-a-Luck must be the murderer.
- The Scarlet Pimpernel had Marguerite, after initially complying with Chauvelin's demands, interfering by warning the Scarlet Pimpernel of danger in the library. Chauvelin discovers this when he finds her earring there.
- In The Searchers, Ethan gives Debbie his medal at the beginning and years later sees it around the neck of the man believed to have kidnaped her. Debbie reappears soon afterward.
- Shoot-Out at Medicine Bend: When Devlin sees Nell wearing his mother's locket, which was one of the items stolen from him, he knows that she must be in contact with the thieves somehow.
- In 1635: The Papal Stakes, the presence of "uptime" casings for shotgun and rifle rounds for use in 20th century gun designs reveals the presence of United States of Europe agents and groups, in investigations by Cardinal Borja's assistant Pedro Dolors into the whereabouts of Pope Urban VII.
- In Beautiful Darkness, Ethan finds Lena's iconic and personalized charm necklace on a beach near the Great Barrier, and knows something must have happened to her and that she passed by that spot.
- Inverted in The Tide of Victory, when Rana Sanga's family was killed by banditsnote the ruins of their carriage contained burned-beyond-recognition bodies that were identified by number, gender, and more durable personal effects. Except... the box his wife habitually used to carry the onions she preferred for cooking was found charred but empty, and the plain little knife she cut them with was nowhere to be found.
- In The Convenient Marriage by Georgette Heyer, the heroine is lured under false pretenses into the home of a notorious rake. She manages to escape unscathed, but loses a distinctive piece of jewelry in the process. This is found at the rake's home by one of her enemies, who later produces it as evidence that she must have been there willingly.
- From Rosemary Sutcliff's novel The Eagle of the Ninth: While staying with the people who took the titular eagle from his father's legion, Marcus removes the eagle during the night and hides it under the banks on the edge of a lake, for Esca to return in secret and retrieve days later, after the two of them have been followed and searched. Unfortunately, while doing so, Esca accidentally drops Marcus' distinctive ring-brooch, already "all but torn out" of Marcus' cloak through the roughness of the aforementioned search. When the natives find it days later, they give chase.
- The Lord of the Rings: Peregrin Took drops his elven brooch while being transported by his orcish captors, in hopes his friends will pick up his trail. The gambit pays off.
- In The Price of the Stars, when General Jos Metadi learns that his daughter Beka was killed when the freighter he gave her several months earliernote crashed, he goes to inspect the site himself; examining a chunk of charred control panel and verifying that what was left of the engines were "standard for the class." Given that he rewired the control panels himself and put considerable effort into keeping the engine upgrades he made in his privateer days off the books, it was obvious to him what had become of his youngest child; so he had what was scraped out of the life-pod sent home for a proper funeral and ordered the wreckage destroyed before the any of it could be scavenged for souvenirs.
- In the book Shakespeare's Scribe, Jamie Redshaw's cane is found with an empty treasury box, having been used to beat its guard. Except it's no longer Jamie's cane. He had bet it in a card game a few days before the robbery and lost.
- Sherlock Holmes: The Hound of the Baskervilles:
- Watson is hiding in an abandoned building waiting for a suspect. The suspect is actually a disguised Sherlock Holmes, who realizes Watson is waiting due to the particular brand of cigarette that he had tossed down before entering.
- The protagonists found the boot used by Stapleton to set the hound onto Henry Baskerville in the Grimpen Mire after he fled, but they didn't find him, and assumed he fell into the mire.
- A Song of Ice and Fire features the catspaw that attempted to kill Bran early into A Game of Thrones, who carried a particular Valyrian steel dagger that, according to Petyr Baelish, belonged to Tyrion Lannister, seemingly implicating him in the murder attempt. This turns out to be false, as later in the books, it's revealed Littlefinger used it as a way to blame Tyrion while exploiting Joffrey Baratheon's desire to please his father. That the thief had that weapon at all is what clues the Starks in to the fact that the attempt on Bran's life was ordered by a member of a powerful House, as Valyrian steel weaponry is very rare and extremely expensive, and certainly not the weapon of your average street thug turned assassin.
- In an episode of Babylon 5 Garibaldi goes to find a witness to an attack but someone gets to him first and kills him. Garibaldi is left only with the body, and what appears to be a coat button which is later identified as coming from the coat of a Centauri royal guard.
- Cold Case: In "8:03 AM", Miller's informant Toomey has a very distinctive dreamcatcher pendant. Over the course of the investigation, the detectives learn that the pendent originally belonged to one of the two victims, who had given it to the second victim as thanks for pulling her out of a dangerous situation. On learning this, Miller realises that the only way Toomey could have it was if he was involved in the murders.
- Subverted in an episode of Due South. There is evidence that a hitman has been watching Fraser's apartment: cigarette butts from his distinctive brand are found near a hallway window in a building opposite where Fraser lives. But the cigarettes aren't stamped out as if the hitman stepped on them, or crushed as if he put them out on the windowsill; they're evenly snuffed, as if the alleged hitman had put them out in an ashtray at an earlier time and then someone else trying to frame the hitman (and Fraser) planted them there - which is exactly what happened.
- Innocent: When Yusuf finds a camera-lens pendant in a secluded wooded area, it makes him suspect that his old friend Taner is in fact alive.
- On an episode of Stargate SG-1, SG-1 goes to a planet they've never been to before and find a pack of Russian cigarettes. When they get back they have a little chat with the Russians about what they were doing there and what they found.
- Star Trek: The Next Generation: After Riker, Troi and her mother are kidnapped by the Ferengi Tog, the bouquet of flowers from Ferengi space Tog brought to Betazed is later found by Enterprise security giving them a good idea who's responsible.
- In The X-Files, the ash from the Smoking Man's cigarettes have made it clear he's somehow involved a few times (one of the first being when it tipped Mulder off that he'd been in The Mole's car).
- Older Than Feudalism: In The Bible, Potiphar's wife gets hold of Joseph's cloak as he runs away from her. She later produces the cloak to support her claim that he tried to rape her.
- In another story, a woman named Tamar loses her husband, and he died without any male heirs. As per custom of that time and place, she is remarried to his brother Onan, who also dies. Next in line is a boy named Shelah, who is conveniently not old enough for marriage just yet. His father Judah tells Tamar to move back in with her parents and wait until Shelah is old enough, at which point he'll be married to her. But when Shelah finally comes of age, Judah has him married secretly to someone else, leaving Tamar out in the cold. Since there are no more brothers for Tamar to marry, she takes matters into her own hands. She disguises herself as a shrine prostitute, and waits for Judah. He promises to pay her a goat for her "services," and she takes his seal, cord, and staff as "collateral" until he can do so. After they do the deed, he goes to get the "shrine prostitute" a goat as promised, but she's long gone, and he's told that no known shrine prostitutes wait there. He shrugs it off and goes on with his life. Three months later, it's revealed that Tamar is pregnant, and Judah sentences her to be burned to death for engaging in illicit sex and shaming the family. Before she's brought to the stake, she sends a messenger with the items she took as "collateral," saying that the man who owns them is the father. Judah recognizes the items as his, and spares Tamar's life, because he realized that she did her duty (providing an heir for her first husband) while he shirked his (giving Shelah to someone else instead of keeping his promise to his daughter-in-law.)
- In Shakespeare's Cymbeline Iachimo "proves" that he seduced Posthumus' wife by showing him a bracelet which he claims the wife gave to him; in reality he sneaked into her bedchamber while she was asleep and stole it.
- In Lady Windermere's Fan by Oscar Wilde, Lady Windermere, mistakenly thinking her husband is cheating on her with Mrs Erlynne, goes to her other admirer's dwellings in a moment of weakness. He isn't there, but Mrs Erlynne arrives there and sets her straight. Both women hide when a group of men including Lord Windermere arrive unexpectedly, but Lady Windermere's fan is discovered on the table, recognised by her husband. Fortunately Mrs Erlynne gives herself up, allowing Lady Windermere to escape unseen.
- In Othello, the title character is convinced of his wife's infidelity when he discovers that her supposed lover is carrying her distinctive embroidered handkerchief.
- In Noob: Le Conseil des Trois Factions some of the protagonists run into an acquaitance who lets the fact that he's doing a quest linked to the game's Big Bad slip. They get him to tell them more, and his first revelation is that he has the mask that the Big Bad is normally constantly wearing in his posession.
- My Little Pony: Friendship Is Magic: In "Rarity Investigates!", a clump of rainbow-patterned hair that matches Rainbow Dash's mane is found at the crime scene on top of an envelope that contained the false message for Spitfire, suggesting Rainbow Dash is the culprit. Rarity realizes it's a Red Herring because one end of the clump has been cut straight with shears.
- In Scooby-Doo! Mystery Incorporated, the very first episode has the kids discover a mysterious locket during their investigation of the crime scene. At the end of the case, they ask the criminal about it, to which he denies any association with. However, Mayor Jones (and possibly Sheriff Stone) seem to know something about it, and a mysterious caller contacts the kids about it when they're hanging out with Angel Dynamite, telling them that this is their first step into a larger mystery. It turns out that Mayor Jones is responsible for making the owners of that locket "disappear", and he was worried that this trope would come into play as he apparently did not get rid of all the evidence. Angel and the mysterious caller are associated with the owners of the locket, but they've had no reason to bring up the case until the kids rediscovered it.
- Star Wars: The Clone Wars: In "The Lost One", it happens twice. At the beginning of the episode, long-dead Jedi Master Sifo-Dyas' lightsaber is found on a wrecked shuttle on the moon of the planet Oba Diah — which, given he supposedly died on Felucia, is odd to say the least. The second time, Anakin and Obi-Wan catch the leader of the Pyke Syndicate in a lie because he's wearing a necklace that belonged to Silman, an aide to former chancellor Finis Valorum — suggesting that he knows something about Silman's fate.
- After Leopold and Loeb disposed of Bobby Franks' body, Leopold left his glasses at the scene. These glasses had a unique hinge mechanism that only a few people in Chicago had at the time, leading investigators to him.
- Deliberately invoked by some criminals who go out of their way to make sure they are identified as being in a specific location at a certain time so as to set up an alibi for a crime they committed elsewhere.