California Code, Probate Code - PROB § 2310

(a) The appointment, the taking of the oath, and the filing of the bond, if required, shall thereafter be evidenced by the issuance of letters by the clerk of the court.

(b) The order appointing a guardian or conservator shall state in capital letters on the first page of the order, in at least 12-point type, the following:  “WARNING:  THIS APPOINTMENT IS NOT EFFECTIVE UNTIL LETTERS HAVE ISSUED.”