Advertisement On Cars Outlawed in California?

Up until about a year ago it was very common to see advertisement on the side of cars here in Southern Calif., particularly on P.T. Cruisers and the new V.W. Bug. What happened? You don't see them anymore. Was it outlawed for being a dangerous distraction?

I mean the cars that were turned into a traveling billboard, not just stenciled advertisement you still commonly see on cars and trucks(like a construction comapany's name and phone).