Characters with signature design trait?

Okay okay I'll start first

Kokoro - Her headgear (known as ear flaps) is ABSOLUTELY needed as her design, like how a Pokemon or Digimon protag can't be seen without their cap or goggles. (It was initially based off that lol) She basically is never seen without one and owns multiple designs of it. If she's not wearing one, chances are she's wearing alternatives like a beanie, hooded blanket or cover with a towel. It's just a running joke that you can't see her headgear-less, lol. I didn't come up with any story behind it, but I'd like to think it was a gift from her late mother and she holds a strong attachment to it to wear it all the time.

Sakane - Not as much as Kokoro but both in-story and among TH, she's always pointed out for her huge scarf? She doesn't have many variation of it either, but it's a really notable thing you see in her design mainly for the size, I assume. She doesn't wear it in her casual outfit, but pretty much wear it in mostly her default outfit, This one also have no story-related reasoning other than a simple design trait.

Kozue - This is more of a physical design trait since you can't wear it or remove it but Kozue without her fang is not Kozue. Same goes for Inugami.

Manami - I wouldn't count this as an accessory but you notice that he is never seen without his green book. _{Inside the book, he kept a photo of his friend that already passed away}

Yunosuke  - Maybe it's not that noticeable but I'm obliged to draw him with his badly-tied necktie in any outfits he have. Apparently he wear one just to look smart. Edit: Another response below mine mentioned about a "smile" being a signature and I think Yunosuke is also counted for that! As stated in his profile, he's always smiling even during serious situation that some actually finds it unsettling that he have no other expressions than smiling despite he can spew out cryptic things when talking lol (And a little fun fact: I always ask people I commission to draw him with a smile because it's the most important thing for his character) Edit again: WAIT....He have more signature design traits than I expected lol but he also must wear his two hairclips no matter what, it's basically the last gift he got from his deceased aunt and he's just never seen without them ever since. The little accessories on his wrists might count as well? 

Adding another character, Takuto is always seen covering his head with a hoodie. There's a (spoiler) reason for that, but let's say he doesn't like showing his face much and that's also why I choose to cover his eyes with the long bangs.

You know I had to really think about the question, as you did mention something they'd never be without, and well, yeah it hit me that Machina here does apply the best, and might be one of two who really fit the prompt to the fullest.

I would have plenty, but I mix up outfits and hairstyles often, I really like changing it up, and since I can't really change my looks up or anything, I live through my characters in that way :p

But Machina here always has that collar. I forget why she even has it, which is probably not the best reason to keep the tradition going if I don't even know why, but well yeah, I specify this in her reference, she must have the collar. And well yeah, she's always had it. She can live without it, of course, but she wouldn't really want to.

Faith is new to me, but that third eye(well I imagine that was the designer's idea.) is really a gem that kinda houses her soul as part of how I do ghosts. Basically she could go without the gem, but it's a big risk to her.

Vivienne is however an interesting case. She's only been drawn with her twintails. Even back when all she was is human Violette before a bunch of universe changes over a few years. Anyway, I never actually had a chance to get art of her where I felt right asking for a new hairstyle, so I mean I always could get her a new one, but at the same time, I really do think I would keep her twin tails, and well yeah, as I type this it really does seem right. So I guess I got three!~

Camilla kinda fits too, because while there's art of her without them, she will most often have a Mega Milk shirt, and there's an in character reason for it, it was a part of how she bonded well with her sister after a troubling childhood and all, so while she's not always in them, they are important to her! And well, when I get a chance, there'll be Mega Milk sweaters, hoodies, bunch of stuff. In universe, but not art, she even has a Mega Milk Apron~

I have quite a lot of characters who may seem to have the same hair style through images, but that's simply because I mostly get freebies over the years, and it's not right to be really demanding about those, unless the one doing the freebies says it's fine to give those ideas.

Ooh, interesting thread! I think I have some of them, even though it's not always super specific accessories! 

• Anselm: It's not already visible since his only outfit visible on TH for now is his 18th century one, but... Anselm always wears a blue coat/vest/whatever and yellow pants/trousers/whatever no matter the period he goes to! Unless the time period really doesn't allow it, but otherwise, he sticks to this specific palette.
• Olivier, Louis & Lucien: They all have signature colours (green, turquoise and yellow respectively), just like their friends (who belong to... friends of mine haha). They cannot be drawn with another colour except for "neutral" tones like black, gray, white and brown. For example, Louis can't wear orange, that wouldn't be Louis :')
  • Also, they also all have signature flowers who match their colours; Lucien has the sunflower, Olivier has the green carnation, and Louis... Louis has the cornflower because I couldn't find a turquoise flower to save my life lmao
• Lilith: Her frying pan appears in most of her artworks! I don't even ask artists to add it, tbh, it comes naturally most of the time and I love it :')
• Moroni: It's similar to Lilith; even though it's less widespread, his white umbrella is his signature item!
  • Story-wise, it was previously his mother's signature item. I have yet to draw her with it tho
• Tobie: His hairstyle got pointed out a lot, so I guess it's iconic of him? He has 3 different outfits but the hairstyle always stays haha
• Harahel: Harahel without an unholy amount of flowers on him isn't Harahel
  • Alternatively, some people have pointed out that his cigarette was iconic of him and I like that haha

Chrysler always wears a golden chain with a diamond shaped thing with NY engraved in it ^.^ (It's cuz he was a Hetalia oc based off NYC haha) also his extremely long hair could count too xD

Cyanide would always have rings on his hands that are C and N because his chemical formula is CN- Also his hair is a cyan color cuz why not lol, though the color if cyanide isnt that bright; instead it's more of a darker blue (basing this off his design b/c I can't remember the exact details atm)

Saccharin has a specific design trait, which is his eyes should not have that white shine in them, if this makes sense. Usually yandere characters eyes lose that shine when they're in yandere mode lol, so I just decided he would just not have the shine at all (so permanent yandere mode? Lol jk). It'll just stay green with the top of his pupils darker. 

Nitrous has a couple design traits but the most important one would be his smile. He has a permanent smile regardless of emorion; his eyes and eyebrows can express other emotions but his lips would always smile. I sort of related it to how nitrous chemical is also laughing gas. Other design specifics would be his earring (there for fun tbh lol), and both the N2O on the back of his jacket and the 44 on the back of his racing outfit. Former is his chemical formula and latter is molecular weight.

Skye has dyed ties on her hair, and although she's not my only ic who has this, her dyed ties has more I'd a meaning than the other oc; in fact her whole hairstyle (and by extension, pretty much her outfits and personality) is a break from her previous life and now that she can do and wear whatever she wants, shes taking full advantage of that.

Henri is always wearing his eyepatch due to something in his past that made him lose the eye on that side ;; Other design choices would be him always in long sleeve clothing since he's really pale.

Lysande always has the hairclup and the earring on his left side. The earring was from a failed bet and the clip was because at one point he got something stuck in his hair there so he tried to fix it by chopping the whole thing off there XD His coworker hated how it looked and triedto fix it himself lol; he does a decent job but since the stray hairs seemed to bother him, Lysande holds it back with a clip. Now one side is just always gonna be longer and the clip would stay and it's become his signature hairstyle lol

Poyo here has the old style kirby cheeks with the three lines. I thought it was cool lmao

The dark lipstick. I throw a fit whenever someone forgets to draw it on her orz.

even in universe she just always wears that hoodie unless she's sleeping...... she went to a tropical country wearing the godforsaken thing because she was like 'ITS MY BRAND' . even in Cool God Form :tm: she leaves it on... a fashion disaster icon

pearl always wears a yellow bow ! i guess it's the same case of 'young anime protag aesthetic'..... again theres an in universe reason but also? its just cute

not a human char for once but mina's blue bowtie has stayed with her through the many many redesigns ive done of her ! it's been her one central design point since..... 2013 i think?

Leon's buck teeth must always be showing. Mouth open? Mouth Closed? Always. No exception.