Just like all of us, characters often have traits we associate with them. It could be a physical object like always holding a cup of coffee or a pack of cigarettes. It also could be a dialogue pattern or a commonly used expression. For example, in my series, one character is known for constantly stating that there's more than one way to skin a cat. It could also be a physical trait like someone who walks with a skip or is bowlegged.
It doesn't matter if characters are major or minor or only around for a short time; there should be distinct traits because this makes them seem more 3-dimensional. The last thing you want is a flat character because this makes them more difficult for the reader to connect with them. And if a reader can't connect with the specific character then they are less likely to care. And if they don't care about the characters, they probably won't likely care about the book either.
If you want an example of character traits, I'd suggest you watch your favorite show and observe the actors and see what specific things you associate with them. Do they have unusual speech patterns? Do they dress uniquely? Do they have a hairstyle that stands out? Do they have lime trees throughout their house? Do they occasionally jump from English to Spanish? Do they carry a baseball bat in their trunk? You know, the usual stuff.
Remember, most character traits come out as you're writing so don't overthink it. They'll show you as you develop them.
