This is activated whenever you receive a message from the server as a notice. This is basically anything beginning with "***" which is sent to you by the server, and the MOTD.
The parameters for the action are as follows: $0 The name of the server which sent you the message $1 The first word of the text sent - probably "***" or "MOTD" or the name of a channel, eg, "&LOCAL" $2- The message