Penal Code § 653
CHAPTER 2. Of Other and Miscellaneous Offenses
Every person who tattoos or offers to tattoo a person under the age of 18 years is guilty of a misdemeanor.
As used in this section, to “tattoo” means to insert pigment under the surface of the skin of a human being, by pricking with a needle or otherwise, so as to produce an indelible mark or figure visible through the skin.
This section is not intended to apply to any act of a licensed practitioner of the healing arts performed in the course of his practice.