The bonds shall be signed by the chairman of the district board, and countersigned by the auditor of the district, and the seal of the district board shall be affixed. The interest coupons of the bonds shall be numbered consecutively and signed by the auditor of the district. All such signatures and countersignatures may be printed, lithographed, engraved, or otherwise mechanically reproduced, except that one of said signatures or countersignatures to said bonds shall be manually affixed. The auditor of the district under this section shall be the county auditor of the county in which the district is formed.