I love the idea, but JFP is correct: highly illegal in most (all, I'm sure) states. If an officer sees that, you'll get pulled over. I guess you could always try to play it off as a short in the wiring or something, but that's a gamble.
Any flashing lights on a vehicle, other than turn signals, are illegal unless it's certified and approved to have them. A friend of mine got in trouble a couple years back for having flashing LED lights on his valve stem caps (tacky, I know).
The charge was impersonating a police officer or something similar
