You know, I don't recall tattoos ever coming up in the Pokemon games. There may be some minor random trainers with them (like the bikers, but I can't remember exactly), but nobody major.
If you think about it, they make a lot of sense- people in the Pokemon universe are already identifying with their 'mons so much they pattern their teams, gyms and lives after them...why wouldn't they take the next step and make those creatures a part of them?