You can put in a web page a icon which will show your jabber presence status by using something like: 
<img src="http://jabber.linux.it/presence/YOUR-JID@jabber.linux.it"
 alt="" border="0" width="16" height="16">

Then add presence@jabber.linux.it to your roster to enable it. If presence@jabber.linux.it is not in your roster you will always appear offline.

Available icons: