It's basically just LEDs lighting up the sign in multiple colors at a frequency adapted to the vehicle speed. You could package it up to look like a regular lig

It's basically just LEDs lighting up the sign in multiple colors at a frequency adapted to the vehicle speed. You could package it up to look like a regular light (that looks white to humans) and a regular traffic camera or surveillance camera. The camera is easy enough to make inconspicuous. The LEDs and processor can be in a regular light enclosure. You just need to find a good excuse for the sign to be illuminated.