It was pretty easy to recognize a crown vic behind me (that's what 90% of the cop cars are around here). Well marked ones (with roof lights and a front plow bar) would obviously be easy to spot, but I could still usually make out the lights hidden behind the grill on unmarked ones.
That being said, why are you so concerned about spotting a cop behind you? Don't drive like an idiot and you shouldn't get hassled for anything other than tint (which you say you don't care about).