34 CFR 681.17: Security and endorsement.

(a) A HEAL loan must be made without security.

(b) With one exception, it must also be made without endorsement. If a borrower is a minor and cannot under State law create a legally binding obligation by his or her own signature, a lender may require an endorsement by another person on the borrower's HEAL note. For purposes of this paragraph, an “endorsement” means a signature of anyone other than the borrower who is to assume either primary or secondary liability on the note.