They're actually called "Fat Caps" and they are the favorite of "graffiti artist" everywhere. I've never used them, but the concept is to lay a lot of material with each pass. They're cheap (10 for 3-4 bucks) and available online at the web site below.

http://www.grafcaps.com/index.php?ma...=index&cPath=1

Regards and let us know what you're painting (lest we think you're a "tagger"!)
Glenn