Used to do this all the time for the period that I was FO. Nothing like walking past some Diamond gate louse seated in Y, miffed that he/she didn't get their upgrade when F is called. I've even been called out on it by said gate louse times once or twice. So much fun...

As for the original topic, I've only spotted medallion tags in airport or airport transit environments. Though, I did sit down at an Orlando Apple store in a mall one time next to an individual who had one his AA Executive Platinum luggage tags on the backpack he brought with him to the store. This was back when I was a DL GM. Got a bit of a chuckle out of it.