Always, nobody deserves to be robbed by those greedy highwaymen.
I actually have a bit of cardboard that says ''RADAR'' with black marker which I put beside the road to warn others of the danger up ahead if I have time.
Or well not always, they often check if people flash and fine those, I usually open my window and use a ''slow down'' gesture until it's safe to flash a bit later on. I've actually stopped people and made em turn around because they were driving in a street that is forbidden in 1 direction for 2 hours a day (for rush hour/ cut-through/against rat running) and the idiots from the local police were ****ing people over further down.
Even if one person doesn't get a fine I'm happy, they can stick their war on the motorist & mobility up their arse.