(a) Bonds shall be executed by the manual or facsimile signature of the chairman and by the manual signature of the secretary of the authority involved.
(b) Coupons attached to the bonds shall be executed by the facsimile signature of the chairman. In case any of the officers whose signatures appear on the bonds or coupons shall cease to be officers before the delivery date of the bonds or coupons, their signatures shall nevertheless be valid and sufficient for all purposes.
(c) Each authority shall adopt and use a seal in the execution and issuance of bonds, and each bond shall be sealed with the seal of the authority involved.