Registered securities may be assigned in blank, to bearer, to a specified transferee, or to the Secretary of the Treasury for redemption or for exchange for other securities offered at maturity, upon call or pursuant to an advance refunding or prerefunding offer. Assignments to “The Secretary of the Treasury,” “The Secretary of the Treasury for transfer,” or “The Secretary of the Treasury for exchange” will not be accepted unless supplemented by specific instructions by or in behalf of the owner.