I have seen similar applications for house windows. They are actually pretty cool. It doesn't seem practical for a motorcycle though. At least not when there are already flip up kits being made by several companies.I dont agree with what your doing at all but I figure if you are really determined to do it you wont care what ne one says. That being said Polarized lenses are actually an amazing thing, you might have to dig on the web a bit to find the right thing but if u can get 2 polarized pieces of plexiglass or glass or plastic (not sure if plexi glass or plastic can even be polarized) and u put them together poles reversed then nothing can be seen threw them. So if u have only one sheet on ur plate it would ust look like a tinted cover, then somehow fashion a second piece, turned the opposite way, to fall on the 1st then Kazam no light passes through making ur tag blocked. I probly didnt make any sence just now but it does work.
My question is this: if you are going to break the law anyway, why even bother going through the trouble making a contraption to hide your plate? Just try and outrun the police car; if it doesn't work out, you are going to jail in either case, and the money you save not putting gadgetry on your bike can either be applied towards your bail or your casket.