Making signwritter work on big sites

A little shortcomming I encountered when I was looking at signwritter to use as an email obfuscator (http://dominiquedecooman.com/blog/how-obscure-email-and-other-text-using...) on a 3 Million node site. All files are written to the same directory. Which would mean I have 3M imagefiles in one dir. So this meant disaster.
Here is a little patch that solves the problem.
Can you confirm that this is the only place in the script were the directory name is needed?

Btw thanks for this well written module.