Bonds or notes of the United States, or other obligations which are unconditionally guaranteed as to both interest and principal by the United States, may be pledged and deposited as collateral security in lieu of corporate sureties in accordance with the provisions of the Treasury Department regulations in 31 CFR part 225, Acceptance of Bonds Secured by Government Obligations in Lieu of Bonds with Sureties. Cash, postal money orders, certified checks, cashiers' checks, or treasurers' checks may also be furnished as collateral security in lieu of corporate sureties.