An allonge to promissory note is an actual sheet of paper or document firmly affixed to a promissory note or negotiable instrument that may contain additional endorsements. The written endorsements on the allonge are considered a part of the bill itself and are treated as such in loan proceedings.
An allonge to promissory note is different from an assignment. An assignment in this context is what gives a party the legal designation and right to move forward with legal action on a property, whereas an allonge is an endorsement that allows you to collect on the promissory note.