Everyone has tells and some of them are pronounced enough that its easy to peg who they are playing even if they drastically switch up their roles.

They can be
common typos
common reactions to criticism
How they argue in character (this is graatchs biggest tell everytime you end up in an IC disagreement he just switches into lawyerly batter the hell out of the conversation mode regardless of his role)
Gear they favor
Spots they rest up in
General approach to preping
General approach to hunting/risk
The way they phrase prayers and seek PC interaction
Writing style in roles