Yeah regular in the UK. Two flashes of head lights followed by sometimes the driver doing a straightened palm with a downwards movement and if you
make eye contact they will have the look of The Fear of God in their eyes, then you defo know there is a speed trap somewhere ahead
You can be fined for warning oncoming motorists about a speed camera van in the vicinity so you have to be careful and have an excuse like there was a
wasp in the car and I was trying to swat it