You can spray paint your back windows black if you want, let alone any darkness of tint you want. heck alot of SUV's have VERY dark tint in the back now a days anyway. Its only the front windows that have the severe tint restrictions. If you are worried about people seeing the brand of speakers you run, tint the shit out of the back and install them so they cant be seen from the windshield/front windows. If you are worried about people knowing you have any speakers at all, keep the vehicle looking stock and nobody will be looking inside it anyway.
What I love is the guy who slams his truck, bags it, slaps 24's on it, stickers all over the place, hot paint, etc... and then wants a stealth install on his stereo. lawl