Vehicle Code § 39007
DIVISION 16.7. REGISTRATION AND LICENSING OF BICYCLES
After December 31, 1976, no bicycle retailer shall sell any new bicycle in this state unless such bicycle has legibly and permanently stamped or cast on its frame a serial number, no less than one-eighth inch in size, and unique to the particular bicycle of each manufacturer. The serial number only shall be stamped or cast in the head of the frame, either side of the seat tube, the toeplate, or the bottom sprocket (crank) housing.