Hi, I've writen a new module. Please check it out :)
signature.module (tested with Drupal 4.6.2)
1. Makes user signatures dynamical, that is, if user change his signature in his profile, after each of his/her posts will be new a new one signature.
2. Shows signatures not only after comments, but also after nodes.
3. Allows define content types (and at once comments for them) where signatures should be seen and where not.
4. Usability benefits - 'cause each time user adds a comment, he/she don't have to pull down signature to the end of his/her comment.
5. Comments are styled another way than the post itself, and it's customizable from 'administer->settings->signature'.
Since function of displaying signatures is hardcoded into comment.module, that module needs to ba patched, to pull out this functionality to external module. There is a file with explanations how to patch, and already patched 'comment.module' from Drupal 4.6.3.
If you're intrested - you can get it here: www.ultraboy.by.ru/signature-4.6.0.zip .
It's seems to work good, but inside not everything is nice - I'm working on fixing that.
Your feedback is appreciated.