The mayor and council of any city of the third class, for the purpose of paying any sum of money which it may now or hereafter be required to pay by the judgment or decree of any court of record, may issue coupon bonds of the city, payable in such lawful money of the United States as they may provide, which shall run for a period not exceeding twenty years, may carry interest payable annually or semiannually, at a rate not exceeding six percent per annum, shall be signed by the mayor, countersigned by the city treasurer, attested by the city clerk, and shall bear the seal of the city.