(a) Bonds shall be executed by the manual or facsimile signature of the chairman of the corporation and by the manual signature of the secretary of the corporation.
(b) Coupons attached to the bonds shall be executed by the facsimile signature of the chairman of the corporation.
(c) In case any of the officers whose signatures appear on the bonds or coupons shall cease to be such officer before the delivery of the bonds or coupons, their signatures shall nevertheless be valid and sufficient for all purposes.
(d) The bonds shall be sealed with the seal of the corporation.