I normally bright my friends, or give the "5-0" sign with my hands.

 

Flashing highs for sure.

 

What integrate said. Sometimes I've seen people put an index finger to the sky and wave it in a horizontal circle (a la sirens), but that can easily be confused with "we gotta flip a u".

 

I would have to agree with the majority here. Flashing your lights is a common practice to alert someone there are cops ahead. You dont see that too much any more.
kris

 

Exactly... by my house.. when people start flashing the lights or high beaming you.. Slow down there's a cop ahead...

 

I use the military thing, I make a fist and hold it up for the "HOLD" symbol.

 

I didn't know of the military connotation, but this was the sort of thing of which I was thinking. Get their attention (lights, "V", or whatever) then hold up a fist.

In any case, it'll only work if everyone understands it, so we need to promote the idea. I'm on it.

 

I'll do that.

 

This is why God invented radar detectors.

An interesting happened to us Saturday in Claremont at the start of the Mt. Baldy meet. I was last in line to turn left to the road to the start up the hill. We had just left Asif's Baskin & Robbins parlor. The cop was going the other way, looked at us, did a quick U turn, ducked in right behind me, and got on his radio, changing channels furiously. We all pulled over to sort out and form up and he pulled just in front of us at a 45

 

I've seen the 5-0 signal a bunch of times, but it's hard to see sometimes, and you need both hands to do it. If you're going the opposite direction, then flashing the high beams a few times usually works to slow people down.