If you're looking for a way both to obstruct 90% of the view out of your back windshield and provide a beacon to po searching for cars to pull over, I am pleased to offer you one of AGPtek's bumpin' & grindin', sound activated LED stickers. The equalizer lights rise, fall, and generally gyrate to the beat of whatever music you blast while driving.
Stickers themselves are thin sheets that attach via adhesive tape to vehicles' rear windshields, side windows, or anywhere with access to 12VDC power and riders looking to bring the party to the interstate. AGPtek notes it is also possible to covert the low-consumption LEDs' power source to a cigarette lighter. When rocking to the rhythm of the house, lights flash in shades of blue. Each sticker measures about 17-1/2" long x 4-1/4" tall.
Note: Anyone with music-controlled car stickers will likely receive feedback about them from other drivers on the road. For those inclined respond to this feedback with panache equal to that of the equalizer lights, I would recommend a rear window LED messenger.