An association may invest its funds in the valid warrants or bonds of any city, town, county, school district, port district, or other municipal corporation in the state of Washington which are issued pursuant to law and for the payment of which the faith and credit of such municipal corporations is pledged and taxes are leviable upon all taxable property within its limits. The aggregate of the investments of an association in any issue of such warrants or bonds shall at no time exceed five percent of the amount of its savings accounts.