39 C.F.R. § 762.29 – Endorsement of disbursement postal money orders by payees.

(a) General requirements. Disbursement Postal Money Orders shall be endorsed by the payee or the payees named, or by another on behalf of such payee or payees as set forth in this subpart B. The forms of endorsement shall conform to those recognized by general principles of law and commercial usage for the negotiation, transfer, or collection of negotiable instruments.
(b) Endorsement of disbursement postal money orders by a financial organization under the payee's authorization. When a Disbursement Postal Money Order is credited by a financial organization to the payee's account under his authorization, the financial organization may use an endorsement substantially as follows:
Credit to the account of the within-named payee in accordance with payee's or payees' instructions. Absence of endorsement guaranteed.
A financial organization using this form of endorsement shall be deemed to guarantee to all subsequent endorsers and to the Postal Service that it is acting as an attorney in fact for the payee or payees, under his or their authorization.
(c) Endorsement of disbursement postal money orders drawn in favor of financial organizations. All Disbursement Postal Money Orders drawn in favor of financial organizations, for credit to the accounts of persons designating payment so to be made, shall be endorsed in the name of the financial organization as payee in the usual manner.