I got some sticker paper at Walmart. I have a design about as wide as a business card, but a little shorter.
It has my logo on the side and text that says “Owned and operated by Tucson Pinball. For maintenance requests please message us on Facebook or email (email address”.
I have been putting those on games that aren’t at my main location. At my main location I have a small whiteboard for players to write down issues and my friends will just send a message.