Other than the fact that she doesn't really have the normal body build of a rat and is the size of a dog, I'd say her trademark is her fire tail that never goes out, rain or shine!
(Apologies if this thread have been created but why didn't I have ideas for threads when I still had my premium/search button lol)
So! One of my favorite part of a character design is them having a certain design trait or accessory (or just anything like hairstyle, clothing, item, etc) that are strongly associated with a character--they wear/hold them most of the time regardless of outfits, situations (or heck, you can spot it even if the character appears as a silhouette) or they absolutely have that as a part of their character and it's either rare or looks strange if they are seen without one? As one would say, well, their "signature" or "trademark" in a form of design.
Do share as many characters as you want here, I'd love to know! (Also feel free to share if the said design trait is just an extra addition to their design or have a certain story or reason to them)
Prime examples would be: Any form of hats, plushes, hair clips/necklace/bracelets, maybe the character is always seen with a ponytail? And many others