Users of JSesh can create their own signs, using softwares such as Adobe Illustrator or Inkscape (which is free).
JSesh can import signs from :
true type fonts (see fontforge for a free editor) ;
SVG files : SVG is a relatively recent format for vector graphics. It's very powerful and complete. Currently, JSesh understands SVG files if the sign is drawn in black over white. You can edit SVG files with a number of programs; one of the best free ones is Inkscape, which has the advantage of being multi-platform.
For compatibility with my previous software (tksesh), it can also read: