The securities and any coupons bearing the signatures of the officers in office at the time of the signing thereof shall be the valid and binding obligations of the district, notwithstanding that before the delivery thereof and payment therefor, any or all of the persons whose signatures appear thereon shall have ceased to fill their respective offices. Any officer authorized to sign any security or interest coupon, at the time of its execution and of the execution of a signature certificate, may adopt as and for his own facsimile signature the facsimile signature of his predecessor in office in the event that such facsimile signature appears on the security or coupons, or both, appertaining thereto.