RCW 43.21A.640

All revenue bonds issued hereunder shall be legal securities, which may be used by a bank or trust company for deposit with the state treasurer, or by a county or city or town treasurer, as security for deposits in lieu of a surety bond under any law relating to deposits of public moneys. They shall constitute legal investments for trustees and other fiduciaries other than corporations doing a trust business in this state, and for savings and loan associations, banks and insurance companies doing business in this state. All revenue bonds and all coupons appertaining thereto shall be negotiable instruments within the meaning and for all purposes of the negotiable instruments law.