Police speed control

Whenever I drive on the road in Holland and I spot a police car with a radar gun, I'm allowed to informl the local radio station so they can warn other drivers about the situation.
Is this allowed in your country too?

I'm not allowed to give light signals to other drivers and warn them, but I am to the the above.
How about your place?

Since you only got bicycles, boats and Klompen in Holland, why does the Police have cars? You should demonstrate against this. Not fair. I'd emigrate as soon as possible if I were you. So sorry for you guys.