Quote Originally Posted by Schmedlap View Post
Does anyone know how the custom began of flashing one's headlights to inform other motorists about police cars lying in wait for speeders? This is something that predates the internet, cell phones, or other electronic mediums for quickly spreading a code or signal, so I surmise that it was spread by word of mouth or something equally non-technological.

What does this have to do with this thread? I suspect that similar signals are used in Iraq and Afghanistan that coalition forces are unaware of, but that are common knowledge to the locals.
clothes hung on a line a particular way, kids playing a certain game or in a certain place, fruits or veggies set in a certain order. Nothing like word of mouth to turn the inane into operational tactics

as to your initial ? I remember when I was a kid being told about it in relation to big rig truckers,
They flash lights to let you know when its clear to move over, or if someone's around