Legal Question in Constitutional Law in California

No, aside from some very narrow exceptions. They can probably ban nudity and profanity, for example, as well as incitements to violence. There may be other similar exceptions I'm not thinking of at the moment. Otherwise, any regulations have to be content-neutral.

Mr. Hoffman needs to go back and review his law school Constitutional Law class notes. Although commercial signage is still subject to some First Amendment protection, all commercial speech may be much more heavily controlled, regulated and restricted than other speech. Content-based restrictions, and even content-based bans on certian types of commercial signage have been upheld. Think about bans on liquor and cigarette billboards; they are a classic example. In fact, using Mr. Hoffman's example of incitement to violence, it would actually be far more constitutionally permissible to ban commercial ads for fast food, than to order a sign taken down that said, "Cops are an occupying army. Take arms against them!"

I stand corrected. Mr. McCormick is right. There are still limits on the government's authority to regulate what billboards can say, but that authority is broader than I had originally described.