I wish what you said about arrest wasn't true. I can see that happening here in the States. In a variation of wackiness. It is now illegal to warn oncoming drivers of speed traps. If you flash your lights and a police officer observes you, you are subject to a $400 fine. This is the same fine you can receive for honking your horn for other than safety reasons. If you honk your horn to wave at a friend, $400...
We now have Flash Traps here in the state of Washington. One officer sits at one intersection checking for speeders. Another officer sits on the next bridge and watches for people flashing their lights.
I made up the term Flash Traps. Maybe we can start a Meme... Someone else has probably already come up with it.
Surely anyone flashing their lights and "observed" would use the simple defence that they were flashing for one of its two legally sanctioned purposes - to indicate "I am here and perchance you appear not to have noticed", or "I intend to overtake".
The "observer" would then have to testify that there was no possibility that the intended recipient of the signal had failed to notice either the presence of the flashing vehicle (representing a potential danger or obstruction) or was signalling an intention to overtake a slower vehicle. And as we all know, coppers never lie under oath.
And as we all know, coppers never lie under oath.
Many years ago when I had a passing interest in UFOs, there were some stories of police seeing these objects. When two police officers are in agreement and testify in a court of law, the odds are you’ll get a conviction every time. However, when they testify about seeing flying saucers, those odds drop to zero.