Tattoos cause gut reactions upon first sight. Similar to the reaction a guy gets when another attractive guy walks in who could be their competition, or when you see a girl you find attractive and you feel that hormonal jerk in your body -- a dopamine shot or an adrenal shot.
I believe this happens with tatoos because tattoos resemble scars. And scars illicit involuntary responses in the nervous system. Scars, evolutionarily speaking, are evidence of surviving conflit. They signal strength and danger to other men in the area, similar to how a strong physique signals strength except that scars are past tense. Once we think rationally tattoos are just tattoos and we get over it, but the effect exists if only temporarily.
I'm betting that women feel this too, and I always think that anything non-verbal that I pick up on, women probably pick up on it more strongly.
That's what I'm thinking. Tattoos are sexually appealing because of these reasons.
Tribal body paint has the same effect, and seems to be the evolutionary origin of the modern tattoo:
Native people untouched by modern civilization use body paint during demonstrations, warring periods and during mating rituals.
I don't think it's really a coincidence. It's kinda tempting to get tribal body paint done just as an experiment before going out on a Friday night just to see if it makes any difference. Maybe a sleeve or something.