California Code, Elections Code - ELEC § 20008

Any paid political advertisement that refers to an election or to any candidate for state or local elective office and that is contained in or distributed with a newspaper, shall bear on each surface or page thereof, in type or lettering at least half as large as the type or lettering of the advertisement or in 10-point roman type, whichever is larger, the words “Paid Political Advertisement.” The words shall be set apart from any other printed matter.

As used in this section “paid political advertisement” shall mean and shall be limited to, published statements paid for by advertisers for purposes of supporting or defeating any person who has filed for an elective state or local office.