There is always the old trick we used when we were kids. Just throw a bunch of mud on the license plate and let it dry!

 

Good concept but there are a lot of much cheaper options out there. I'd stick with the photo spray personally (less $$$ and you can do your bike, your car, your buddy's bike and car. . .) . Running from the po-po is a big no no when you finally get caught.
http://www.phantomplate.com/
http://www.specterguard.com/
http://www.loover.com/
If you insist on being retarded. . . still cheaper.
http://www.plateflipper.com/

 

ive said it before, if you really want to do that just hang your plate with key chain rings. that when you take off it flips up from the wind. when you stop gravity brings it down. cost 20 cents...lol *disclaimer* hoedogg does not approve of or suggest running from cops.