Section 30951 Of Chapter 4. Regulation From California Food And Agricultural Code >> Division 14. >> Chapter 4.

. It is unlawful for any person to own, harbor, or keep any dog over the age of four months, or to permit such a dog which is owned, harbored, or controlled by him to run at large, unless the dog has attached to its neck or leg a substantial collar on which one of the following is fastened:
  (a) A metallic tag which gives the name and post office address of the owner.
  (b) A metal license tag which is issued by the authority of a county, city and county, or any municipal corporation for the purpose of identifying the dog and designating the owner.