Start here:
http://signature.statseb.fr/index.py You'll need to Register, so click that link, then input your Boinc name , password, and Cross-Project Id. You can find that on your WCG "My Profile" page. From there, you can customize as you see fit.
It's so easy, even I was able to do it just now.
/edit: Easy, but still not quick enough on the draw.