Different states have different laws. In some cases they have what I think are called "secondary" laws, where the cop can only cite you if he's already pulled you over for a more serious offense, like speeding. Here where I live, you're technically supposed to have a front license plate, but I'm pretty sure they can't pull you over if you don't have one... they can only cite you for no front plate if you're already pulled over for something else. Maybe tinted glass is also one of those types of things in some states.