The treasurer of the city shall be the custodian of the several funds. All payments from the funds shall be made by him only upon vouchers signed by two persons designated by the board of trustees. A duly attested copy of the resolution of the board of trustees designating the persons and bearing on its face specimen signatures of the persons shall be filed with the treasurer as his authority for making payments upon the vouchers. No voucher shall be drawn unless it shall previously have been allowed by the board of trustees.