I'm having problems with the signatures for my users. To show the signature in their posts/topics the users have to click "edit" and check the Signature box, even if it already was checked when making the topic. This happens all the time, even when replying to a topic. In the admin tools the allow signature and dynamic signature box is checked.
First of all a test account for your forum would help so we can take a look. Also, I guess it's a problem either in post.asp or post_info.asp, so if you can post links to .txt versions of those files, we could look for the problem.