Cal. Bus. & Prof. Code § 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 “D.O.,” or any other terms or letters indicating or implying that the person is a physician and surgeon, physician, surgeon, or practitioner under the terms of this or any other law, or that the person is entitled to practice hereunder, or who represents or holds themselves 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. No person shall use the words “doctor” or “physician,” the letters or prefix “Dr.,” the initials “M.D.” or “D.O.,” or any other terms or letters indicating or implying that the person is a physician and surgeon, physician, surgeon, or practitioner in a health care setting that would lead a reasonable patient to determine that person is a licensed “M.D.” or “D.O.”
(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.” or “D.O.”:
1. (1) A graduate of a medical or an osteopathic medical school approved or recognized by the medical or osteopathic medical board while enrolled in a postgraduate training program approved by the board.
2. (2) A graduate of a medical or an osteopathic medical school who does not have a certificate as a physician and surgeon under this chapter if the individual meets all of the following requirements:
  1. (A) If issued a license to practice medicine in any jurisdiction, has not had that license revoked or suspended by that jurisdiction.
  2. (B) Does not otherwise hold themselves out as a physician and surgeon entitled to practice medicine in this state except to the extent authorized by this chapter.
  3. (C) Does not engage in any of the acts prohibited by Section 2060.
3. (3) A person authorized to practice medicine under Section 2111 or 2113 subject to the limitations set forth in those sections.
4. (4) A person holding a current and active license under this division or any initiative act referred to in this division, to the extent the use of the title is consistent with the act governing the practice of that license.
5. (5) A person whose use of the word “doctor” or the prefix “Dr.” is not associated with any claim of entitlement to practice medicine or any other professional service for which the use of the title would be untrue or misleading pursuant to Section 17500.