It could mean a million things...lots of guys are out there that look good, but would be ruined if they got a tattoo....She could mean that she finds them sexy on certain people, namely the tough rugged type...and maybe you're just not that guy, which is fine, dont try and be someone you're not....
The thing is, dont take if personally...I dated a girl that said the same thing...she totally loved the ghetto lookin tough guy with tattoos...but not on me....Im a tall, dark, and big Italian...But Im also extremely smart, and she agreed it wouldnt look good on me...though I look like a guy not a lot would mess with, I just still wouldnt look that great with tatoos on me...Maybe if I was the stupid type that goes around collecting money or other errands for certain "higher people" like some of my relatives...then ok...but im not that type...do I take it personally, no...My uncles even told me that that life is not for me...Though I do have a temper some times and im bigger than a lot of guys, I'd rather be a teacher and live a long life rather than go around breaking guys arms and never knowing when im gonna be done....
Sorry for the rant, just making a point....some guys wear tats well...others dont...but either way, its just a certain taste of hers, almost like a fetish, but if shes not acting on it, then thats all it is...I wouldnt worry about it