This is activated whenever someone on a channel you are on leaves irc. Normally, the display would show:
*** Signoff: <nickname>
but, of course, you can change this. If <nick> is your own
nickname, then the action will be taken when you exit
from irc. The parameters are as follows:
$0 The channel from which the person signed off
$1 Nickname of person who left irc
$2- Text of Signoff message.