I agree with the above two posts. If we don't announce it, how will you ever know it's there?
Let's assume we don't announce anything.
Random player X finds some new thing and gets a hat (lets say). Player X tells Player Y. Player Y gets it as well, and tells Players 1, 2, 3, 4, and 5 - who all do the same thing. However, they fail to tell anyone else and when we remove the limited edition thing, a bunch of people start to complain because we didn't announce it.
No fun.