I saw the same thing about the sharpie. Don't know of any other fine point markers around at that time. I researched the "Marks A Lot" pens, but came up empty.
The signature does look really good. This could have been made with an Autopen. I'm not saying it was, but it's a possibility. Here is a nice read about the Autopen.
http://gizmodo.com/archives/retro-gadget-tuesday-the-autopen-015872.php
