Bonds issued under this chapter bearing the signature of the president or other authorized officer in office on the date of the signing thereof shall be valid and binding obligations; provided, that before the delivery thereof and payment therefor, any person whose signature appears thereon shall have ceased to be an officer. The validity of any bonds shall not be dependent on, or affected by, the validity or regularity of any proceedings relating to the acquisition or improvement of the system for which such bonds are issued. The resolution authorizing bonds may provide that the bonds shall contain a recital that the bonds are issued pursuant to this chapter, which recital shall be conclusive evidence of the bonds' validity and of the regularity of the bonds' issuance.