Some interesting bits of that California law:
- our Virginia stickers are illegal per that law - it makes exemptions for stickers in the corners, but not in the center. Good thing I'm not planning any cross-country trips.
- It makes exemptions for rear-view mirrors, hinges and some other bits, but not for defroster wires or third brake lights (in my 240SX coupe, as in many cars, the third brake light is mounted in a pod which sticks up and blocks a section of rear glass).
In short, I think one could make a case that the law is unenforceable.
Speaking of Virginia stickers, I had a friend who lived somewhere in the rest of Virginia but spent a lot of time in Fairfax county. His county required no tax decal. He constantly got pulled over for it. Thankfully, Fairfax county doesn't require one anymore, either.
I've had no problems with laws or the people who enforce them, here, though. YMMV.