Signature Device

A tool, weapon, or object that all members of a certain group (usually Differently Powered Individuals) possess. Often a Transformation Trinket.

Naturally, groups using these as means of identification tend to consider it a vendetta-worthy offense for an outsider to be seen with one, even if it was not pried out of cold dead fingers of a legitimate owner.

Not to be confused with the Autopen.

Anime and Manga

 * Air blades (roller blades?) in Air Gear.
 * The Beyblades from Beyblade
 * Zanpakouto in Bleach. (Dolls for the Filler Arc's Bounts.)
 * Knightmare Frames from Code Geass.
 * Digivices for the Digidestined from Digimon
 * Diaries (of all sorts) in Future Diary.
 * The eponymous Gundams
 * Controllers in Hunter X Hunter each have one.
 * The Vongola (Mare/Acrobaleno Pacifiers) Rings from Katekyo Hitman Reborn.
 * The Guns from Letter Bee that the Letter Bees all use.
 * Pokeballs and the Pokedex from Pokémon
 * Tennis rackets in Prince of Tennis
 * The transformation wands from Sailor Moon.
 * Yu-Gi-Oh!: Duel Disks in all their shapes and forms.
 * The Books from Zatch Bell

Comic Books

 * Green Lantern Rings for the Green Lanterns and the other corps
 * Anything starting with the word "bat" in Batman.
 * Legion flight rings from The Legion of Super Heroes

Film

 * Star Wars: Lightsabers, for Jedi

Literature

 * In the Dresden Files, the silver, anti-magic sword and unstainable grey cloak of the Wardens is this.
 * Played with - focii help focus a wizard's magic in large part because they believe it will. However, there are also items imbued with power. Harry's are the staff and wand and duster (and gun).
 * Wizards robes are both a symbol of office and needed because magic interferes with electronics, including heaters.
 * In the Sword of Truth it's the ... Sword of Truth. For the Seeker of Truth.
 * At the palace of the prophets, the Rada'Han is this for wizards.
 * Confessors' dresses.
 * Higher-rank wizards wear simpler clothes.
 * Defenders of the Lord Rahl wear special weapons with his crest.
 * War Wizards' gear is this.
 * The rings in the lips of the female slaves of the Imperial Order.
 * Darken Rahl's curved knife.
 * The Mord-Sith Agiel. Various colors of leather outfits, too.

Live-Action TV

 * Morphers for the titular Power Rangers
 * The Swords that the Shadow Chasers use.
 * The sonic screwdriver and TARDIS of Doctor Who and the Time Lords
 * The transporter has appeared in every incarnation of Star Trek.
 * "Garage Door Openers" for all Stargate team members.
 * Transformation Trinket belts for Kamen Riders.

Tabletop Games

 * Dungeons and Dragons settings often use such trinkets - some magical, some not.
 * Holy symbols. They almost never are exclusive for clergy - sometimes lay worshippers wear them as a sign of devotion - but practically anyone wearing what you recognize as a holy symbol of some deity almost certainly either is a priest thereof or at least belongs to the church hierarchy.
 * Drow nobles get House Insignia - an amulet with their heraldic device and some magical powers, mostly of utility sort. Typically they double as magical "keys" for most security magic on their estate(s), obedience enchantments on mounts, and so on - and are booby-trapped, so that an outsider who took one from the rightful owner's body faces a nasty curse rather than freebies.
 * Forgotten Realms has enchanted pins used by Harpers. Cormyr has common enchanted items for army (Purple Dragon's ring, Commander's ring) and War Wizards (War Wizard's cloak) that double as a "badge" of office and "pass card", in that they are compatible keys to certain generic wards (such as barracks and armories) enforcing different levels of security clearance. Witches of Rashemen have their enchanted masks - though there's a wide variety of those, they have a common recognizable look.
 * Al-Qadim got amulets of sorcerous societies. Again, those are both used as identification marks and have magic keyed on them, starting from the spell broadcasting a message (used mostly as a request for help) to all bearers of the amulet in range.

Toys

 * Masks in Bionicle.
 * Zoids in...you guessed it!...Zoids

Video Games

 * Keyblades in Kingdom Hearts.
 * Player Pins for Players in The World Ends With You
 * In Castlevania, the Belmontsalmost always have the same set of secondary weapons: throwing knives, throwing axes, cross, holy water, and stopwatch.

Western Animation

 * The Guardians and their keytools in ReBoot
 * The communicators designed by Robin and Cyborg in Teen Titans, which actually serve as a plot point.
 * The Assault Weapon Systems in Centurions.

Real Life

 * Most stock costumes, which are themselves generally examples of Truth in Television. Particularly:
 * Scrubs, stethoscopes and clipboards for doctors
 * Guns and badges for police officers
 * Cellphones, PDAs or Bluetooth headsets for businessmen