Bonds herein provided for shall be issued in such amounts as may be necessary to provide sufficient funds to pay all costs of acquisition, construction, establishment, extension or equipment, including engineering, legal and other expenses, together with interest to a date six months subsequent to the estimated date of completion. Bonds issued under the provisions of this article are hereby declared to be negotiable instruments, and the same shall be executed by the proper legally constituted authorities of the municipality or county commission, and be sealed with the corporate seal of the municipality or certified by the county commission, and in case any of the officers whose signatures appear on the bonds or coupons shall cease to be such officers before delivery of such bonds, such signatures shall nevertheless be valid and sufficient for all purposes the same as if they had remained in office until such delivery. All signatures on the bonds or coupons and the corporate seal may be mechanically reproduced if authorized in the ordinance or order authorizing the issuance of the bonds.