Found this to be amusing. If you do possess United States Notes (lawful money), you can redeem them at Treasury. Bet that process goes smoother than redeeming FRN’s.

“All outstanding United States Notes, which were issued in denominations of $1, $2, $5, $10, $20, $50, $100, $500, and $1,000, may be redeemed at face value by the U.S. Treasury Department. Payment would be made in the form of a Treasury check.”

http://moneyfactory.gov/usnotes.html