Someone asked, so here it is.
Simply wrap [img] tags around this:
Code:
http://status.icq.com/online.gif?web=ICQNUMBERHERE&img=27
Where "ICQNUMBERHERE" is your number
And it'll give that little button that's green when you're online and red when you're offline. It updates automatically, so you don't need to change anything after that.
Done!