One of my parents neighbors took this a step further -- he bought a surplus blue Crown Vic, put a yellow day glow strip on one side and parked it on his land near the curb.
At a glance, it looked like a state police cruiser.
I once saw a full-size, flat plastic dummy that looked like a police car from the side. Slowed everybody down too. It was only clear it was a dummy as you passed it.
At a glance, it looked like a state police cruiser.