I was looking for the legal requirements for tint when I stumbled upon the CHP website. They've got a three page list of stuff thats not legal.
I wonder if they enforce most of it cause I know more than a couple California natives who could suffer heavy fines. Read it, even if you're not Californian.
Note: The law says officers don't have to test your exhaust with a dB meter, but rather use their own judgement. Then you have to fight it out in court.
(at the bottom of the page)Remember - FTBC (failure to be cool) is not a crime! California Highway Patrol