The "Stackexchange" site list on the right-hand side of the blog is missing its link for "Area 51"
Area 51 has not been announced outside of meta so the link was excluded from other references. It's probably the worst kept secret in history, but the appearance of the icon is supposed to be a bit of a teaser. Honestly, nobody has asked me about it apart from the meta-folken.
Area 51 will be announced to the public very, very soon (and linked from the blog).