Associations may prohibit commercial signs and flags from being posted (i) in the common areas and (ii) in separate interests. Civ. Code §1353.6(a)

A commercial sign is one that displays a message on behalf of a company or individual for the intent of making a profit. It is economic in nature and usually has the intent of convincing the audience to purchase a specific product or service. Signs advertising property for sale or for lease constitute commercial speech. Fourth La Costa v. Seith

In addition, obscenity and fighting words may be restricted.