I wanted a different ASCII art signature for my @ubuntu.com email address than I had for my personal account, so I took a couple minutes, and hacked one up together pretty quickly. It's only 3 lines, which is appropriate for an email signature I believe. It's not perfect, but it conveys the idea.
,-O Ubuntu Linux O ; http://www.ubuntu.com `-O Linux for Human Beings
If you would like to leave an ASCII art improvement of the above in the comments, please wrap them in <code></code> tags.