honestly I think tats in general are nasty so id have to say turn off. but there's a reason its called "tramp stamp". cause theyre usually so small only someone in the middle of doing you from behind can get a close enough view of what it is to be able to appreciate it, which is why theyre called tramp stamps.
I like what Vince Vaughn said about lower back tattoos in 'Wedding Crashers':
"Might as well be a bulls-eye"
Honestly I don't mind them, I just might find the girl a bit sketchy as to how promiscuous she is. But I definitely don't find them "hot." If I had a choice, I like girls without them. You can't improve on the female form, it's perfect the way it is.
I think its just as they say, tramp stamp. If a girl is going to get a tattoo on her lower back, then I'll usually assume she's a tramp and avoid her... or hit on her, depends on if I'm looking for an easy one night stand or not, lol.