But why would he get a tattoo of someone he does not seem to care one iota about? Didn't even have a convo with his best buddy when she went missing.
IMO the tattoo is not Laura and has zero to do with her.
I think the experience affected him more than he wrote in texts. Perhaps he didn't care about LB, but I would argue that the reality of what was going on around him - and in which he was complicit - woke him up. That tattoo will keep him awake to that reality. And, honestly, who else is it? It's practically the same shirt she has on in the photo, long hair, smile, wings. It isn't a photo of her face - so the tattoo guy took artistic license, can't be anyone else.
ETA: It's not in evidence anyway so it's rather irrelevant.