Wash. Rev. Code § 35.36.010
The mayor, city comptroller and city clerk of every city of the first class may each severally designate one or more bonded persons to affix his or her signature to any bond or bonds requiring his or her signature.
If the signature of one of these officers is affixed to a bond during his or her continuance in office by a proxy designated by him or her whose authority has not been revoked, the bond shall be as binding upon the city and all concerned as though the officer had signed the bond in person.
This chapter shall apply to all bonds, whether they constitute obligations of the city as a whole or of any local improvement or other district or subdivision thereof, whether they call for payment from the general funds of the city or from a local, special or other fund, and whether negotiable or otherwise.
RCW 35.36.010