I love the idea of them not responding to the new name that goes with their new life until the character is accustomed with it. As for a mark, perhaps a mole or scar on like the arm or other part of the body that they either had early on from their first life, or something received at/around the end of their first life? Just an idea. I originally was thinking of like a birth mark, but honestly I feel that's been over done a little, but it's your RP idea so don't read too much into my one opinion(s) until there are (hopefully) more people who are interested. :)