I have a similar story to KR.
Boyfriend is up for the weekend, sorority house is full, so we drive down to the river and are parking. (May I mention it's 11 AM) Well before things get too involved, a cop car pulls up behind us and we freak. We (ahem) readjust ourselves and wait for the cop to come up to us....and wait and wait. After sitting there for, oh, 10 minutes, boyfriend goes back to the cop car to see what is up. He comes back shaking his head and chuckling. Turns out the officers just pulled in to enjoy some pizza and didn't even notice us.
Oh, and Pitt people take note...just a couple months ago, coming back from the South Side I got pulled over at a checkpoint under the Birmingham Bridge, mainly because I didn't understand the officer's bizarre "stop - no, go - no, slow" sign language. I had to do the nose touching, breathalyzer, whole deal. I think they felt somewhat silly when I blew a .01.