20 CFR § 726.106 - Type of security.
(a) The Office shall determine the type or types of security which an applicant shall or may procure. (See § 726.104(b).)
(b) In the event the indemnity bond option is selected, the bond shall be in such form and contain such provisions as the Office may prescribe: Provided, That only corporations may act as sureties on such indemnity bonds. In each case in which the surety on any such bond is a surety company, such company must be one approved by the U.S. Treasury Department under the laws of the United States and the applicable rules and regulations governing bonding companies (see Department of Treasury's Circular - 570).
(c) An applicant for authorization to self-insure based on a deposit of negotiable securities, in the amount fixed by the Office, shall deposit any negotiable securities acceptable as security for the deposit of public moneys of the United States under regulations issued by the Secretary of the Treasury. (See 31 CFR part 225.) The approval, valuation, acceptance, and custody of such securities is hereby committed to the several Federal Reserve Banks and the Treasurer of the United States.