I have no tattoos. I can't think of anything that I like enough.
I have a good friend who does Ironman's (you run a rough ridin' marathon, then ride like a hundred plus miles on a bike, and swim a couple miles), and he has a tat of the Ironman "M" logo thing. That's pretty cool. That really means something, and symbolizes a huge accomplishment.
I also know some marines who have served in combat and have tattoos. I am not a "military" type guy, but if you have served in combat and got a tattoo to commemorate it, then you earned it bro. I'm not man enough to object.