An insurer may invest in bonds, notes, or evidences of indebtedness of any state of the United States or province of Canada, or any political subdivision thereof or any agency or instrumentality of any of the foregoing, which are payable from revenues or earnings specifically pledged for the payment of the principal and interest on such obligations, and for the payment of which a lawful debt service fund or reserve fund has been established and is being maintained.
SDCL 58-27-12