Expressive Accessory

An item that changes based on the expression or condition of its master, though it usually has no reason whatsoever to do it.

Expressive Shirt is a Sub-Trope.

Compare to sister tropes Expressive Hair, Expressive Mask and Eye Glasses.

Examples of Expressive Accessory include:

Anime and Manga

The headbands on Ninin ga Shinobuden.
Taking this concept to its logical extreme, it's not uncommon for Humongous Mecha with humanoid faces to mirror their pilot's expression. Tengen Toppa Gurren Lagann's mecha even lip sync to their pilots' dialogue. From the same series, Yoko's skull hairpin sometimes expresses her emotions, like when she realized that the men desperately needed a bath, the pin made a ">_<" expression while Yoko was holding her nose and pretty much doing the same.
- Also, note this (NSFW) little incident...
Chouhi from Koihime Musou wears a tiger hairpin that always mimics her expression.
In Lucky Star, Tsukasa has her bow droop when she's sad in episode 18 and the OVA, and spike up when she's shocked in other episodes.
Princess Snow's snowman pendant in MAR. It's a magic pendant, though.
Yuki's cat-belt… thingie in Saki.
The skull on Kuromi's forehead in Onegai My Melody does this.
Minami Shimada's Hair ribbon, as well as Himeji's bunny hair clips.
Pita-Ten has the toy bunnies in Misha's hair frequently mirroring her emotions. The fancomic The KWM Championship (included in the Pita-Ten Official Fan Book Vol. 2) played with this with Misha, after losing an important battle to Koboshi (It Makes More Sense In Context), pretending to be as cheerful as ever...while her hairbunnies glare in a rather unsettling manner.
Heihachi from Samurai 7 has a little doll attached to the hilt of his sword that sometimes changes to reflect the general mood Heihachi was in at the time.
Kuromi in Onegai My Melody and sequels. Her black joker-hat has a skull logo that corresponds to her mood change.
Shugo Chara: Amu's hair pins change whenever she character changes, with what she's changing to depending on who she changed with. Most other characters usually have a new accessory pop up out of nowhere.

Comic Books

Asterix's winged helmet.
Adam Warren has used this in several of his works. Considering that most of these involve high tech adventures, there are some allowances. Sometimes a tag on the shirt expressly says that it can do this.
- When he was illustrating for Gen 13, the winged skull tattoo on Grunge's chest exhibited Expressive Shirt tendencies.
There was a character in The Mask who was a huge fan of “Big Head” (that's what everyone calls whoever is wearing the mask at the time) and had a picture of Big Head on the back of his jacket. After he actually got the mask himself, the picture on the back of his jacket changed to his own face, and basically became this trope.
In Batman, the "ears" on Harley Quinn's hat often go up or down like dog ears depending on her mood; may overlap with Expressive Mask.
- Or Expressive Hair, as without the hat her twintails do the exact same thing. They're probably stuffed in there.
Dilbert's tie.
Wade Duck's inflatable water toy from U.S. Acres.
In Groo the Wanderer, the head of the Minstrel's lute changes into a different object in every panel. Admittedly, not necessarily based on his emotional state, though.

Fan Works

In the Ace Attorney fancomics on this blog, the pin on Phoenix's hat tends to change its expression to match his. Same with the face-like scar on Kristoph's hand.
One of the most stereotypical Common Mary Sue Traits is eyes that change color to reflect different emotions. Why anyone would want to have their emotions so blatantly on display is a mystery.

Web Comics

Zeetha in Girl Genius wears a headband with a face on it that mirrors her facial expressions. For example... Otherwise identical faces on her harness don't do this, nor those on her swords. Later it turned out that this works remotely (with the face disk separated from its headband), and well enough to read her lips when she spells out a message. There are some hints of this being an artifact of God-Queens era.
- Similarly, Buck from Buck Godot: Zap Gun for Hire has a belt which sometimes changes to an appropriate expression for the situation.
- More generally this is a quirk of Phil Foglio's style and can be found in other works as well, including XXXenophile.
The hat of Eric in Loserz. He himself is unaware of this, as it says only "Star Wars" when he's not wearing it, although his friends occasionally notice it change.
The Zombie Hunters has Jenny's signature, much-loved orange bear hat.
Eerie Cuties even mentioned Layla's skull-shaped "emotive hairpin" on the cast page.
Homestuck: The expression on Nepeta's cat hat matches her own.
Precocious' Tiffany wears a smiley-face pin whose expression occasionally changes to match its wearer's mood.

Western Animation

Wade the Duck on the U.S. Acres segments Garfield and Friends wears an inner tube with a ducky on it that mirrors his facial expressions. This trait carried over from the little-known U.S. Acres strip.
- Jim Davis must have liked this trope. In the Garfield Halloween special, Garfield wears a pirate hat with a skull and crossbones that mirrors Garfield's expression. At one point when the boat Garfield's in with Odie capsizes, the skull and crossbones jumps off the hat and swims away.
In Disney's version of Little Toot, the title character (an anthropomorphic tugboat) had a steam whistle that mirrored his expressions.
The Chuck Jones cartoon The Bear That Wasn't, based on a book by fellow Looney Tunes director Frank Tashlin, has a factory foreman whose photo ID has the same expression that he has.
Unterbheit minion Catclops of The Venture Bros has a single cat on his forehead instead of an eye; the cat generally shares his expression.
On My Little Pony: Friendship Is Magic, Apple Bloom's bow is like this, drooping when she's in a funk (as seen near the beginning of "The Cutie Pox").
Sir Pentious from Hazbin Hotel has a top hat with an eye and mouth that mimics his expressions. It's even Lampshaded by Cherri Bomb in the first episode.

Video Games

In Paper Mario, the clouds Lakilester and his girlfriend rode on matched their expressions.
When Kouri of the Visual Novel Brass Restoration is in her plain clothes, her bear purse mirrors her expression.
BlazBlue: The Booby Lady's hair pin is an animate (or possibly living) tiny panda. It occasionally moves on it's own, sometimes even leaping between her cleavage after a match (with her laughing about it).
Monkey Island: Meathook's skull tattoo may be something of an edge case, since he does that on purpose.
Occasionally, Suwako's hat in the Touhou series. Her defeat picture in the fighting games, for example, has its googly eyes crying in pain. Fanworks, naturally, take this to the extremes, to the point that her hat has gained its own Fan Nickname of Pyonta.

Real Life

Truth in Television: Mood Rings. Allegedly.