Such bonds by their terms shall be made payable on or before a date not to exceed ten years from and after the date of the issuance of such bonds, which latter date may be fixed by the ordinance directing their issuance or by resolution and shall bear such interest as may be provided in the ordinance ordering the improvement, not exceeding eight per cent per annum, which interest shall be payable annually or semi-annually as may be provided by the ordinance ordering the improvement, and each bond shall have attached thereto, interest coupons for each interest payment, such bonds shall be numbered from one upwards consecutively and each bond and coupon shall be signed by the mayor and attested by the city clerk; provided, however, that said coupons may, in lieu of being so signed, have printed or stamped thereon facsimile of the signatures of said officers. Each bond shall have the seal of the city affixed thereto and shall refer to the improvement to pay for which the same is issued and to the ordinance ordering the same. Each bond shall provide that the principal sum therein named and interest thereon shall be payable out of the local improvement fund created for the payment of the cost and expense of such improvement and not otherwise. Such bonds shall not be issued in any amount in excess of the cost and expense of such improvement.