If the district is a city, the bonds shall be signed by the mayor if there is one; otherwise by the president or chairman of the governing body, and countersigned by the clerk. The seal of the district shall be affixed to the bond. The coupons shall be signed by the treasurer by his engraved or lithographed signature.

If any officer whose signature or countersignature appears on the bonds or coupons ceases to be such officer before the delivery of the bonds to the purchaser, his signature or countersignature is nevertheless as valid and sufficient for all purposes as if he had remained in office.