California Code, Business and Professions Code - BPC § 2054

(a) Any person who uses in any sign, business card, or letterhead, or, in an advertisement, the words “doctor” or “physician,” the letters or prefix “Dr.,” the initials “M.D.,” or any other terms or letters indicating or implying that he or she is a physician and surgeon, physician, surgeon, or practitioner under the terms of this or any other law, or that he or she is entitled to practice hereunder, or who represents or holds himself or herself out as a physician and surgeon, physician, surgeon, or practitioner under the terms of this or any other law, without having at the time of so doing a valid, unrevoked, and unsuspended certificate as a physician and surgeon under this chapter, is guilty of a misdemeanor.

(b) Notwithstanding subdivision (a), any of the following persons may use the words “doctor” or “physician,” the letters or prefix “Dr.,” or the initials “M.D.”: