I'll admit up-front that I have a pretty strong revulsion toward tattoos on the purely physical level. When I see them, I don't see a iconic imagery or cool Chinese calligraphy or anything, I just see pain. Indeed recently psychologists have documented cases of tattooing as self-harm, as an new iteration of cutting on oneself. Perhaps they are now receding back to the alienated subcultures from whence they came.
Once tattoos had a specific anti-social purpose; before they achieved their current semi-respectability, these marks of Cain served to show that one was unwilling to play along with society; one literally branded oneself as an outcast, voluntarily. Or perhaps a tattoo was supposed to prove that you had enough stature and undeniable talent (as a rock star or an athlete or whatever) to rise above what anyone might say about you. Or it was an emblem of solidarity amid a tightly-knit group, like a group of sailors or something. If you inflate and generalize all those motives you probably have an explanation of the 1990s tattoo boom, which in the process nullified what tattoos once connoted and left them signifying only that you were desperate enough to permanently scar yourself to be trendy.
Of course, everyone with tattoos always insists how personal they are, and there must be some truth to that. But still they seem a symptom of the loss of faith in subtler, richer means of communicating things about oneself -- to others and even to oneself. It's a sign of a crisis of belief. A tattoo is perhaps a way to signal that you really mean something; it's a way of swearing on someone's life, only you substitute your own skin for that someone. It's a drastic way of committing oneself, one that seems to suggest that just your word isn't enough to show you really mean something. Tattoos are a way to make communication seem less like bullshiting and more like action -- doing something instead of just yapping about how much you love your girlfriend or how cool you think your car is or how into some band you are -- but the 1990s proved tattoos could be a form of bullshit too.