They do that a lot on the BKK-NRT flights. The sticker is a must at the UA check-in area.

As for the rumors of the Baggage security check in BKK, it's much to do about nothing!!! I noticed the security searching more of the locals travelling than "Farangs". The security line was brisk as I got there around 4:30am. FWIW, I spent more time on the Immigration line than I did checking in on the UA882 flight.