In a bar add a well positioned box, unlockable safe, with your personal detail.
Add a FLIC inside with "push on your own risk".
Use it to turn on some good spotlights on this person, play any attention sound over your PA and grab the persons face on CAM and cast it to all video equipment in the bar. In the message there is a clear "Next round is on ME!" notification. It will sure make your bar stand out from all the competitors which still have the old ship bell hanging to rust.
Or use it a a tip notifier. Our waiter call on the terrace.