Usage: announce [on/off/player name | block/unblock]
The announce command will cause you to be notified when anyone logs
in or out, if you set it to on. You can also set it to notify you of
entry and exit of specific players, eg "announce Buddha" will let you
know if Buddha logs in or out.
With the block argument, it will block other players from seeing you log
on or off. The unblock argument reverses that.
With no argument, it will tell you who is being announced to you.