The bonds to be issued, as provided in section 71.470, shall be in denominations of one hundred dollars or some multiple thereof, and shall be payable to bearer not later than twenty years from their date, and shall bear interest from their date at a rate not exceeding six percent per annum, payable annually or semiannually, such interest payments to be evidenced by annexed coupons, and said bonds shall not be sold for less than ninety-five percent of the face value thereof and shall not exceed in the aggregate the limit of indebtedness herein specified. Such bonds shall be signed by the mayor or chairman of the board of trustees and attested by the signature of the clerk of the municipality with the seal of his office affixed thereto. The interest coupons may be executed by affixing thereon the facsimile signature of said clerk.