Do you flash your headlights at oncoming cars to warn them of cop cars?

[Joe Republic]

When you pass by a parked cop car clearly waiting to pull over speeding cars, do you flash your lights at the next few cars you seeing coming the other way (towards the cop) to warn them?

I love it.  It's actually probably saved me from a ticket more than once.  I've paid it forward many times, and will continue to exercise my freedom of speech to do so.