I have a black tee shirt with SHERIFF in 3 in high white lettering across the back. It is left over from the olden days when I was a volunteer reserve in the local sheriff dept. Just for fun a few years back I wore it while biking. Received so much greater passing room from cars. It was great for a few rides until buddy mentioned that, out on the rural roads where I usually ride solo, I might be a mow down target for a cop hater.
For this technology to be effective the cops should be unmarked.