i've known that for a long time.In DC, they dont use speed traps that often
anymore,now its cameras(22 in all) and they will add 10 more.

 

ive known since the first minute i started driving

 

i've know it since i started to drive also. we also use it in our part of jersey to warn about the deer that like to run out in front of your cars at night.

there was a woman who flashed an oncoming cop about a speed trap, got a ticket and went to court to fight it. she got off on the charge. they basically ruled that if a cop can be acting sneaky and hide to catch speeders, others can warn them to slow down and that flashing the light could have meant 1000 things, like deer in the roadway, so you can't just assume it meant cop ahead

 

My dad taught me that when I first started driving. But you have to try to not make it so obvious, especially at night, because one of my friends warned the oncoming traffic by flashing his brights, and the cop saw it and pulled him over.