... and they didn't want to bother with concealing them. Just googled it now and apparently that's the case, lol:

http://www.vulture.com/2014/08/justin-theroux-leftovers-chat.html

So, back to The Leftovers. Are those your tattoos on your back?
Those are my tattoos, correct.

Wow, you’ve really tatted up.

I have. I’ve been concealing them for years. But it was really more a question of, Hey, you’re doing a TV show — do you really want to get to the makeup chair four hours before everybody else at five in the morning and go to the trouble of removing them all with makeup? Let’s just say that this guy has some tattoos and leave it at that. Which actually worked out, because the kid playing my son is has tattoos, too, so thematically, it kind of works.