Related Clues:

• Collector's item?
• Poker night marker
• Payer's promise
• Debtor's promise
• Promising letters?
• Debtor's onus
• Poker pot paper, perhaps
• Promise of repayment
• Gambler's debt, so to speak
• Letters on a note
• Promise of a sort
• Letters on a chit
• It might be called in
• Paper in a pot, maybe
• Letters denoting debt