Possible Clues:

• Evidence of sale concerning place in theatre, we hear
• Record pie rising before tea ¿ it's proof of ownership!
• Getting right article back ahead of time
• A written acknowledgement
• Acknowledgment about chair for speaker
• Ticket stub, e.g
• It often says 'Thank You'
• Proof one's settled right round westward part
• Acknowledgement
• Right about returned item -- proof of purchase required