The board may provide for the execution and authentication of bonds and notes by the manual, lithographed or printed facsimile signature of officers of the board and, in the case of bonds, by additional authentication by the Treasurer as trustee. If any of the officers whose signatures or countersignatures appear upon the notes, bonds or coupons cease to be officers before the delivery of the notes, bonds or coupons, their signatures or countersignatures are nevertheless valid and of the same force and effect as if the officers had remained in office until the delivery of the notes, bonds or coupons.