California Code, Penal Code - PEN § 26300

(c)(1) Any peace officer not listed in subdivision (a) or (b) who was authorized to, and did, carry a firearm during the course and scope of his or her appointment as a peace officer shall have an endorsement on the officer's identification certificate stating that the issuing agency approves the officer's carrying of a concealed and loaded firearm.

(2) This subdivision applies to a retired reserve officer if the retired reserve officer satisfies the requirements of paragraph (1), was a level I reserve officer as described in paragraph (1) of subdivision (a) of Section 832.6, and he or she served in the aggregate the minimum amount of time as specified by the retiree's agency's policy as a level I reserve officer, provided that the policy shall not set an aggregate term requirement that is less than 10 years or more than 20 years. Service as a reserve officer, other than a level I reserve officer prior to January 1, 1997, shall not count toward the accrual of time required by this section. A law enforcement agency shall have the discretion to revoke or deny an endorsement issued under this subdivision pursuant to Section 26305.