California Code, Penal Code - PEN § 33415

(a) The sale to, purchase by, or possession of silencers by agencies listed in Section 830.1, or the military or naval forces of this state or of the United States, for use in the discharge of their official duties.

(b) The possession of silencers by regular, salaried, full-time peace officers who are employed by an agency listed in Section 830.1, or by the military or naval forces of this state or of the United States, when on duty and when the use of silencers is authorized by the agency and is within the course and scope of their duties.

(c) The manufacture, possession, transportation, or sale or other transfer of silencers to an entity described in subdivision (a) by dealers or manufacturers registered under Chapter 53 (commencing with Section 5801) of Title 26 of the United States Code and the regulations issued pursuant thereto.