It's not really talked about in this edition, and wasn't really discussed in-depth in 4th edition either. But many uses of credsticks and ID verification systems use biometrics to make sure that you're the authorized person. So the biometric reader accessory for your commlink can act as that verification system. It's also an effective locking mechanism, of course, but when you're meeting up with someone who can't see you but wants your SIN to run a background check (this is a super-paranoid Mr. Johnson) they might ask you to scan a thumb or something. If you're making an online purchase, you might have to verify your cred with a thumbprint or something as well.