The bonds must be signed in the name of the director by the manual or facsimile signature of the director. Interest coupons attached to the bonds must be signed by the facsimile signature of the director. The bonds may be issued notwithstanding that the director signing them or whose facsimile signature appears on the bonds or the coupons has ceased to hold office at the time of issue or at the time of the delivery of the bonds to the purchaser.