Well, you have to be caught flashing first. If you've passed the trap, you just about have to flash an oncoming cop to get busted. Now, what would they do? Probably make a u-turn and pull you over. They'll find something to detain you enough to make it a hassle.
So, don't flash the cop.
I used to flash when in more rural areas. In the city/ghetto, no one knows what you're doing. It's pointless around here.