That is a nice machine. Those little Sony Trinitron displays are a pleasure to look at. Unfortunately 5xx machines weren't sold in the UK so I've never had a chance to lay hands on one, but the Trinitron tube is used in the Macintosh Colour Displays.

My Colour Classic has a similar thing with the sticker, except it's sticker is just the Quicktime logo on the bottom right of the front of the machine.