I had an Ohio trooper pull up beside me once and flash 5 fingers twice, as in 55mph (back when that ridiculous law was in effect), and drive on. Needless to say, I slowed down. I am used to cops using blue lights, so when he was coming up behind me in a white car with reds on top, I thought it was a fire department vehicle. SURPRISE!
Another time, an Atlanta motorcycle cop did the same thing on rainy morning as I was weaving through traffic.
Another time, early in the morning around 0200, I had a Glynn County cop on I95 just flash his overheads as if to say 'cool it' and didn't pull me over.
Another time, on I26 outside Charleston, SC, I saw a gray Beemer coming up and dropped down a gear getting ready to race him and made a couple of 'wanna race' moves. He pulled up beside me and I saw "SOUTH CAROLINA HIGHWAY PATROL" on the door, much to my horror. He pulled up beside me, wagged his finger at me and laughed, and just went on. I though I was had, but I think he understood and was cool.
I have had these types of things happen quite a few times so, contrary to the view of some here, they are not all dicks.