In most cases, it's hard for the average observer to guess at a character's occupation just by looking at them unless of course they're actually dressed for work. "Don't judge a book by its cover" may be a bit of a cliche, but it exists for a reason: for many employees, especially white-collar workers, there are no explicit tells that give away their current line of work...
...unless you know what you're looking for.
In fiction and reality, some careers leave a character with subtle hints as to their current or previous line of work, usually (but not always) only visible to the trained eye: maybe there's some kind of habit or quirk of personality that gives away special training; maybe the job left scars of some kind, maybe even some kind of disfigurement; a tattoo or Distinguishing Mark could be involved. If the career is shameful or criminal in some way, the character might try to disguise the traits attached to it - only to end up accidentally revealing it at a pivotal moment.
One way or another, this character has a trait that makes their employment history plainly obvious to people who are either paying special attention or "in the know". In more comedic portrayals, expect the analysis to be completely wrong and the trait to have absolutely nothing to do with the character's line of work.
- In The Great Mouse Detective, Basil, being an Expy of Sherlock Holmes, immediately deduces that Dawson, whom he's just met, is a military doctor just returned from Afghanistan by glancing at the mend on his coat, which is done in a stitch used only by surgeons with a thread native to Afghan regions (identified by its "peculiar pungency").
- Variant: after witnessing Henry's inexplicable connections in Goodfellas, Karen has to ask what he does for a living; Henry claims to be in construction, but a quick feel of Henry's smooth, unmuscled hands reveals this to be a pretty obvious lie. His next excuse? "I'm a union delegate."
- In Men In Black 2, J points out that the now-neuralized K is way too official and much too no-nonsense for a simple postal worker, recognizing his habit of barking rapid-fire orders at his underlings as an obvious remnant of his time with the MIB that even neuralization couldn't erase.
- In Pirates of the Caribbean: The Curse of the Black Pearl, Jack Sparrow's identity as a pirate is given away when Commodore Norrington finds the brand on his wrist (given as punishment for piracy at some point in the past).
- There are various jokes based on this trope that mock the stereotypes associated with various professions, for example:
A sheep farmer is tending his flock when a city slicker rolls up in his BMW, hops out, and asks, "Hey, if I tell you exactly how many sheep you have, can I take one?" The farmer nods, so the city slicker opens his laptop, calls up some satellite photos, runs some algorithms, and announces, "You have 1,432 sheep."Impressed, the farmer says, "You're right. Go ahead and take one." So the city slicker loads one of the animals into the backseat of the car. "Now," says the farmer, "I'll bet all my sheep against your car that I can tell you what you do for a living."A gaming sort, the city slicker says, "Sure.""You're a consultant," says the farmer."Wow!" says the consultant. "How'd you know?""Well," says the farmer, "you come from nowhere even though I never asked you to. You drive a flash car and wear a smart suit. You told me something I already knew. And you don't know anything about my business. Now give me back my dog."
- In the Artemis Fowl series, students of Madame Ko's Personal Protection Academy are given a blue diamond tattoo as part of their graduation, marking them as the finest bodyguards in the world.
- The trope is also somewhat inverted in the first book as Artemis identifies his contact in Ho-Chi-Min City as not being a waiter, drawing attention to the man's well-manicured nails and his voice having a tinge of Oxford about it.
- In James Michener's Chesapeake, Hiram Cater (who is black) is hitchhiking in the southern US in the late 1960s/ early 1970s and is surprised when a white truck driver stops and gives him a lift. The driver says that he has a son serving in Vietnam, and saw that the way Hiram was standing at "parade rest" on the side of the road made it evident that he had also served in the military. Hiram had served in the Marine Corps in the 1950s.
- Discworld: Parodied rather savagely in the Watch books, as Sam Vimes points out "Clues" can have more than one explanation (with a passage specifically riffing on the Sherlock Holmes story "The Red-Haired League"):
He distrusted the kind of person who'd take one look at another man and say in a lordly voice to his companion, "Ah, my dear sir, I can tell you nothing except that he is a left-handed stonemason who has spent some years in the merchant navy and has recently fell on hard times," and then unroll a lot of supercilious commentary about calluses and stance and the state of a man's boots, when exactly the same comments could apply to a man who was wearing his old clothes because he'd been doing a spot of home bricklaying for a new barbecue pit, and had been tattooed once when he was drunk and seventeen and in fact got seasick on a wet pavement. What arrogance! What an insult to the rich and chaotic variety of the human experience!
- Encyclopedia Brown: Encyclopedia figures out that an alleged victim of theft was just lying so he could get insurance money, because the crook, who could have been one of two identical twins, a tennis player or a cashier, was wearing a T-shirt — if the tennis player had been the culprit, one arm would be more developed, while equal arms would incriminate the cashier. Tennis players don't actually have unequal arm muscles, but let's not worry too hard about that little detail.
- In Fahrenheit 451, Clarisse McClellan figures out that Guy Montag is a "fireman" from the smell of kerosene on him.
- The Magicians:
- Magic is performed through extremely complex gestures. Consequently, during his period of self-imposed exile in the real world, Quentin instantly recognizes a fellow Brakebills alumnus by the overdeveloped musculature of her hands and fingers.
- Conversely, in Magician King, Julia begins to notice that magic has a distinctive Signature Scent of ozone that she directly compares to a lightning conductor. Consequently, when Quentin arrives home from his first semester at Brakebills, she knows at once that he's a student magician from the electric aroma around him.
- Moby-Dick has Ismael observe that veteran whalers often have toes missing, or even an outright peg leg. Part of a whaler's job entails cutting the whale into manageable chunks, done with a Blade on a Stick atop the soft, rolling carcass. Errant swipes tend to detach toes and feet.
- The four guilds of London in the first Mortal Engines book have tattoos on their foreheads to denote their allegiance. The engineer guild even takes it a step further by chemically removing all their hair.
- The Three Musketeers has Lady Winter be charged with prostitution in her early days, for which a fleur-de-lis is put on her left shoulder with a branding iron. Cunning minx that she is, she exploits this as proof to Felton that the Duke of Buckingham plans to make her into a concubine.
- Sherlock Holmes specializes in recognizing these traits:
- In his first meeting with Watson in A Study in Scarlet, he quickly determines that Watson is a military man from his stance and bearing, and judging by his deep tan and broken arm (held stiffly), is a veteran of Afghanistan.
- In The Adventure of the Laughing Jarvey (a fanfic by Stephen Fry), he deduces that his current client, Culliford Bosney, is a writer based on the indentation on the inside of his middle finger, caused by constantly holding a pen. When Bosney protests that he could just as easily be a clerk, Holmes replies that he's never known a clerk who wore Lobb boots.
- Combined with Mark of Shame in A Song of Ice and Fire: the Free City of Volantis holds the tradition of marking its slave population with facial tattoos, each line of work represented by a different symbol: soldiers have green tiger stripes, dung-collectors have flies, cart drivers have wheels, prostitutes have a tear beneath the right eye, and so on. While it's possible for a slave to be freed by generous masters, the tattoos make their former status instantly known, guaranteeing that the stigma of being an ex-slave will follow them around for the rest of their lives.
- Early in John Connolly's The Unquiet, a minor character by the name of Dave "The Guesser" Glovsky makes a comfortable living by wagering tourists that he can guess things like their weight, choice of car, or occupation. Observant by nature, the Guesser accomplishes the latter by looking for distinctive signs on the punters, providing a paragraph of tells to look out for: accountants and typists have a slight flattening of the fingertips, chefs have tiny burns and scars on their hands, and so on. It's for this reason that the Guesser swiftly recognizes that his current customer has spent much of his adult life killing people and is immediately nervous.
- Mentioned and subverted in American Horror Story: Asylum: being a former member of the Nazi Schutzstaffel fleeing from justice, Dr Arthur Arden is noted to likely sport the traditional Waffen-SS blood group tattoo under his left arm - one of the many reasons why the character is never seen with his shirt off. However, when Sister Jude gets in contact with Nazi Hunter Sam Goodman, he advises her to avoid trying to get evidence of it lest she end up spooking the target, forcing her to acquire a fingerprint to identify him instead.
- Bones: Brennan is an expert at identifying a victim's occupation based on their bones. For example, one skeleton showed signs of carrying something heavy on one side and had multiple dog bites to the lower legs. She easily determined that he had been a mailman.
- Criminal Minds: Figuring out an unsub's profession can lead to finding their identity, so the BAU team looks for indications in their behavior. Notably, the man who shot Garcia was identified as law enforcement because he insisted on a table with the best vantage point in the restaurant and buckled his seat belt behind him rather than buckling himself in.
- In the Deep Space Nine episode "Necessary Evil", a flashback to Odo and Kira's first meeting features the former interrogating the latter over her suspected involvement in a murder. During a brief digression into work history, Kira hints that she worked in the mines, but Odo immediately refutes this: her hands are far too smooth and clean.
- Subverted in Doctor Who episode "The Sun Makers." During a visit to Company-owned Pluto, the Doctor is continuously mistaken for an Ajack (in other words, a miner). Apparently, the Company's PCM gas doesn't work down in the mines, so Ajacks often come across as flamboyant and pompous by worker standards, making the Fourth Doctor fit the bill perfectly. The Doctor doesn't bother correcting anyone and even uses this misidentification to his advantage when dealing with Gatherer Hade.
- In an episode of Due South, Benton is able to tell that the woman he's having dinner with is not a nurse as she claims to be, as the way she sits at the table implies she spends a lot of time at a computer or typewriter, making it more likely that she is a journalist.
- Ka D'Argo of Farscape sports a number of tattoos indicating his military history, though only fellow Luxans can recognize most of them. In particular, the tattoos on his tentacle beard indicate that he holds the rank of a general; however, he isn't really a general but faked being one in order to save his commanding officer from being tortured by the enemy. More unpleasantly, he also sports metal rings implanted in his collarbone - to be used in order to chain him to the ceiling - a sign of his status as a prisoner of the Peacekeepers. During the crew's temporary alliance with Scorpius in season 3, D'Argo has the Peacekeeper surgeons remove the rings as a sure sign of having moved on from the traumatic events of his imprisonment.
- In The Masked Singer, The Deer was correctly identified as a retired football player because of his poor gait; as one of the judges joked, old footballers have no knees.
- In Taskmaster, one task involved the contestants working out the previous occupation of Hugh, a retiree. Al Murray correctly worked out that Hugh wasn't a manual labourer, because he had soft hands without any calluses.
- In the second season of The Umbrella Academy (2019), Viktor finds himself trapped in the 1960s with a case of trauma-induced amnesia in the wake of the previous season finale. After taking him in, Sissy Cooper tries to help with her guest's efforts to discover his past by checking his hands: she can tell by his smooth palms that Viktor isn't a farm labourer... but he sports calloused fingertips, revealing that he used to a play a string instrument. It's this, combined with his unexpected reunion with Luther, that prompts a few of Viktor's memories to return...
- Worst Jobs In History details quite a few such traits, many of which were quite distinctive:
- Reddlemen were stained permanently red by the ochre they peddled and were frequently mistaken for the devil by superstitious country folk.
- Thanks to carrying around the immensely heavy kegs of water on their backs, water caddies were recognizable by a permanent stoop.
- Tanners were distinguished by the smell of faeces and rotting meat that surrounded them.
- On a similar note, woad-dyers were so pungent that they were forbidden from living within London during the reign of Elizabeth I - and thanks to their habit of testing the alkalinity of their dye by tasting it, their sweat turned blue.
- Castrati could often be recognized even when fully clothed: quite apart from the distinctive high pitch to their voices, the lack of testosterone resulted in them sporting unusually tall, long-limbed frames without body hair.
- "Bufferlasses" charged with buffing cutlery would end up getting the cleansing mixture of dirt and oil splattered all over their hands and faces, sometimes to the point of getting their skin impregnated with it - making it impossible to remove. Also, they stood a very good chance of getting dermatitis.
- Briant and May matchgirls glowed as a result of the white phosphorous they used to make the matchsticks. More unpleasantly, they suffered from an industrial disease called Phossy Jaw that caused their teeth and jawbones to decay as a result of accidental ingestion of the phosphorous, leaving them treated like lepers.
- Lead-based white paint manufacturers who'd been too long on the job suffered from a unique form of brain damage that prevented them from keeping their hands outstretched and level.
- Georgian bath attendants spent so much time in the minerally-enhanced waters of the baths that their skins ended up permanently stained orange, rather reminiscent of fake tanning.
- In various Werewolf: The Apocalypse books, it's mentioned that Burger Fools at O'Tolley's can easily be recognized by the smell of grease and meat even if the embarrassing uniform isn't in view. Veteran "burgermen" also sport numerous minor burns from working the fryers and have become so inured to pain over the years that they frequently expose themselves to absolutely scalding temperatures just to experience real warmth again.
- Final Fantasy XIII: Sazh originally realizes that Lightning is an ex-Sanctum soldier by her outfit, which (while unique) had enough similarities to their uniforms for him to notice.
- During his introduction in The Secret World, Ellis Hill responds to the player's unexpected arrival by grabbing a gun and demanding you identify yourself in an oddly official tone of voice. Once he calms down enough to shake your hand, he approves of your Handshake Refusal, stating that a handshake can give away an identity - and pointing out the obvious wear on his own hands as proof of his career as a metalworker. However, it's his professional handling of firearms and the official-sounding dialogue that hints at his true nature as a Phoenician operative.
- One WWII story tells of a soldier who tried very hard to pass as a civilian while in Europe. He got new clothes, a new hairstyle, learned the local language, etc. One day, while waiting on the curb with two bags of groceries in his hand, a German walks up and basically greets him with "Hi, soldier!" The reason? He had two bags of groceries in one hand because the military ingrains the habit of keeping your other hand free to salute.
- Dr. Joseph Bell, mentor of Sir Arthur Conan Doyle and real-life inspiration for the character of Sherlock Holmes, was capable of deducing at a glance a patient's occupation and the reason for his visit, all before the patient had even said a single word!