The bonds shall be signed by the chairman of the board of supervisors, and the treasurer, and countersigned by the auditor of the county.
The coupons upon the bonds shall be numbered consecutively and signed by the county treasurer.
If any officer whose signature or counter-signature appears on the bonds or coupons ceases to be an officer before the delivery of the bonds to the purchaser, his signature or counter-signature is as valid as if he had remained in office.