Labcoat of Science and Medicine

"Fear not, lab coat fans! This comic isn't the last we've seen of lab coats and the wearing thereof. There are of the utmost importance in a lab / basement where they have yet to be seen ever working with hazardous chemicals."

- The Rant here, El Goonish Shive

In media, there are two sorts of people who wear labcoats; scientists, and medical doctors. As such, a character wearing a lab coat is a good indication that they're involved in either science (and/or Mad Science!), or a medical field. This is despite the fact that in real life doctors and scientist do not normally wear such coats unless there is a reason that they need to keep their clothes clean. In media, this coat is almost always white.

Supertrope to Dressed to Heal which also requires a stethoscope and a head mirror. Compare Einstein Hair, another classic visual cue that screams "Science person!"

Anime and Manga

 * Shinra from Durarara!!, who is noted even by the other characters for not taking that coat off, ever.
 * Icchan from Angelic Layer, who really is a scientist, but most people associate his outfit with "pervert/weirdo."
 * Proffesor Tomoe from Sailor Moon wears one of these in all of his appearances, even in his own house. It's meant to emphasize his Mad Scientist status.
 * All the regional professors in the Pokémon franchise wear these coats.
 * Kakei of Drug and Drop runs a pharmacy and has the lab coat to match. What's less clear is whether he is an actual pharmacist or not.
 * In Nichijou, the Child Prodigy Professor wears an oversized lab coat and tie. Science teacher Kana Nakamura simply wears one over her regular clothing.

Film

 * In G.I. Joe the Rise of Cobra, the scientists working on a particle accelerator all wear lab coats. In real life, particle accelerator operators dress less like movie scientists and more like this.
 * Back to The Future: Doctor Emmett "Doc" Brown wears this until he returns from the future.
 * The Tooth Fairy from The Santa Clause wears a dental lab coat.
 * Dr. Cockroach from Monsters vs. Aliens wears a lab coat, as any respectable Mad Scientist would.
 * Jumba wears a labcoat in the opening scenes of Lilo and Stitch, when he's on trial for creating Experiment 626. He ocassionally wears one in the series when he's working at his lab.
 * Flash Gordon: Both Dr. Hans Zarkov and his assistant, Munson, sport traditional white labcoats in spite of them not actually being in a lab of any kind.

Literature

 * The standard uniform of every Technician, the caste who keep society's machines and computers, and thus, society, functioning in Robert Westall's Futuretrack Five is the classic white labcoat, buttoned in different ways to differentiate between grades of Tech.
 * Invoked by Dr. Sandrisson in Grand Central Arena, whose usual outfit is a white suit of which the coat is tailored to resemble a lab coat.

Live Action TV

 * Practically every character on a CSI series wears a labcoat at one point or another, for the scientist version. And sometimes it's a double, with characters like Doc Robbins and Ray Langston on regular CSI or Dr.Hawkes and Sid Hammerbeck on CSI: NY.
 * Dr. Beverly Crusher, from Star Trek: The Next Generation, is rarely seen without her blue labcoat.
 * Averted Trope by Dr. House, who regularly refused to wear his lab coat. In Princeton-Plainsboro, labcoats are the biggest visual indicator that any given character with whom you're unfamiliar is a doctor and not a nurse or an orderly, as their policy is that doctors need to wear labcoats.
 * Noah's Arc: When Ricky wakes up in the hospital, he sees Junito (who is wearing his labcoat for the first time). The presence of the labcoat lets Ricky know that Junito's there as a doctor, not a visitor, and something serious must've happened to him.

Music

 * Doctor Steel is almost always seen in a somewhat comical-appearing PVC labcoat. His "doctorate" is never really specified, but he shows aptitude in a multitude of disciplines.

Tabletop Games

 * Warhammer 40,000's Fabius Bile wears a lab coat as an obvious marker of his nature as a genius mad scientist. Given that he spends much of his time involved in gruesome surgical experiments or mixing up dangerous alchemical elixirs, it's also of practical use. Of course, this being Warhammer 40k, and Fabius being an amoral monster in league with the Infernal Powers, said labcoat is made from stitched together human skins.

Video Games

 * Doctor Hojo of Final Fantasy VII is never seen without his labcoat. His rival, Doctor Hollander, wears an identical coat in the prequel. It's used to establish their Mad Scientist status and highlight the madness in their scientific endeavors.
 * In The Last Remnant, Rush's parents both wear these. The pair are some of the most well-known scientists studying Remnants in the Academy.
 * Bowman Jeanne of Star Ocean the Second Story wears one when in his pharmacy, and retains it if he joins the party. His special attacks are also themed around pills and medicine to further illustrate his association with this field.
 * In Day of the Tentacle, when Hoagie hires himself as Red Edison's assistant, he is told to "grab his labcoat and get to work", even though the only thing going on in Red's lab is simple mechanic work and Red himself isn't wearing one. (The labcoat figures into a puzzle where it's used to make a kite.)
 * Naked Snake in Metal Gear Solid 3: Snake Eater gets one in order to infiltrate the soviet's weapon laboratories. Guards will be completely fooled by it as long as Snake doesn't start doing suspicious things like crawling around, but other scientists will inmediately trigger the alarm if they see his face.

Webcomics

 * Dr McNinja of The Adventures of Dr. McNinja is either a ninja in a lab coat, or a doctor with a ninja outfit (with mask) under his labcoat.
 * In El Goonish Shive, Tedd, Dr. Germahn and his staff often wear labcoats when working in their respective labs even though they are never seen working with hazardous chemicals as pointed out in the page quote.
 * xkcd combines it with Clipboard of Authority: «Do you know you can just buy lab coats?»

Web Original

 * The titular Dr. Horrible of Dr. Horrible's Sing-Along Blog has a doctorate in horribleness. Of course, when he goes truly evil at the end, his white labcoat is traded in for a blood red one.
 * The Nostalgia Chick introduced us to Doctors C. Block and C. Tease. They have had a few recurring appearances, and even crossed over to other That Guy With The Glasses review videos.

Western Animation

 * Dr. Doofenschmirtz of Phineas and Ferb, the origin of whose doctorate may not have been revealed yet. Played for Laughs as everyone who's not familiar with him thinks he's a pharmacist.
 * Dexter from Dexter's Laboratory is a young Mad Scientist in training. He might not have the formal education, but he certainly has the intelligence.
 * Dr. Scratchensniff from Animaniacs wears one, despite supposedly being a psychiatrist.
 * A perfectly valid piece of attire, since Psychiatrists go through medical school and are licensed to prescribe medication.
 * Johnny Test