CA Penal Code Section 33310

(a)

Every person, firm, or corporation to whom a permit is issued under this article shall keep it on the person or at the place where the short-barreled rifles or short-barreled shotguns are kept. The permit shall be open to inspection by any peace officer or any other person designated by the authority issuing the permit.

(b)

Every short-barreled rifle or short-barreled shotgun possessed pursuant to the provisions of this article shall bear a unique identifying number. If a weapon does not bear a unique identifying number, the Department of Justice shall assign a number which shall be placed or stamped on that weapon.