California Code, Vehicle Code - VEH § 17456

Proof of compliance with Section 17455 shall be made in the event of service by mail by affidavit of the plaintiff or his attorney showing said mailing, together with the return receipt of the United States post office bearing the signature of the defendant.  The affidavit and receipt shall be appended to the original summons which shall be filed with the court from out of which the summons issued within such time as the court may allow for the return of the summons.

In the event of personal service outside this State, compliance with Section 17455 may be proved by the return of any duly constituted public officer, qualified to serve like process of and in the state or jurisdiction where the defendant is found, showing such service to have been made.  The return shall be appended to the original summons which shall be filed as aforesaid.