by Randy Carey:
A note is a legal document. Requirements will be dictated by State law. Seek legal counsel guidance.
by Richard Insley:
Should the borrower default and you find it necessary to sue for judgement, it will probably be necessary for the sheriff to serve your defaulted borrower with a notice of the court proceeding. Since that can't happen inside a P.O. box, your attorney will probably advise you to use physical addresses on contract documents.