I'm familiar with the basics of multi-factor authentication. Now I'm trying to understand how a physical signature, as written on, say, a check or a credit card receipt, would be classified:
Is it a knowledge factor (something you know), in that you know how to write your signature (and someone else can learn it)?
Is it a possession factor (something you have), because it's physically encoded in the muscle memory in your brain cells and the way your hand holds a pen?
Is it an inherence factor (something you are), because the ability to produce it can't be taken away from you and it's (sort of) hard to change?