20 CFR § 416.320 - Evidence of authority to sign an application for another.
(2) If the person who signs is not a court appointed representative, he or she must submit a statement describing his or her relationship to the claimant. The statement must also describe the extent to which the person is responsible for the care of the claimant. This latter information will not be requested if the application is signed by a parent for a child with whom he or she is living. If the person signing is the manager or principal officer of an institution he or she should show his or her title.
(b) We may, at any time, require additional evidence to establish the authority of a person to sign an application for someone else.