When they look for a cop-beater, guess who they'll go to first ?
It's good thing, then, that there are very specific symbols and designs used by such individuals in their tattoos. All one has to do to avoid trouble is simply not get those tattoos. The only cops who would still give you trouble, in America at least, would be of the "dumb asshole" variety.
TL;DR - Nobody bats an eye at tats in the US anymore, so long as you're not sporting a Swastika or actual gang ink.