[spoilers] Lucas and his tattoos

[Byatil]

I think it was just a reminder for her of the photos Kachimov had shown her. She says "your skin" with a sense of shock, because it's such a physical reminder of how much the man she once loved has changed. She will presumably have some knowledge of Russian prison systems, and of course... she didn't know why Lucas had been locked up until Katchimov decided to tell her. It would have been a horrible shock for her, to discover that not only had Lucas changed in both personality and physical appearance, but that he had lied to her for all those years.