All laws and acts of Assembly, exempting the loans, bonds, or other evidences of indebtedness of, or issued by any county, city, borough or incorporated district of the Commonwealth, from the payment of taxes for the use of the Commonwealth, be and the same are hereby repealed, so far as provides for such exemption; and all such loans, bonds, or other evidences of indebtedness heretofore or hereafter issued or existing, shall be liable for the payment of the taxes now or hereafter imposed by law for the use of the Commonwealth upon public loans or other moneys bearing interest: Provided, That this act shall not apply to any bonds negotiated into the hands of innocent holders.