Cop crow
A cop car, usually highway state patrol, that sits empty on the side of the highway with it's lights off. Akin to a scare crow to scare crows away from the crop, a cop crow scares civilians into compliance with the speed limit to deter speeding.
I was speeding on the 15 north until I noticed a cop car and slowed down then when I realized that it was a cop crow, I sped back up.