What? It doesn't appear, at least not for us.
Ugh. Seriously? I've seen them every time, I guess then because I own the bricks, it will only show when I'm in the minigame, or maybe it only shows it to me. I didn't know nobody else could see it, I just thought nobody bothered reading or got into a habit of asking. I swear minigame-related events cause more problems each day.
In that case, we should probably work on either fixing that message or informing everyone who the boss is some other way. Forcing everyone to pick their class before the boss is not a good strategy; I've found the information very helpful myself.