In the Drupal comments/ signature system, there is a usability problem with the signature.
The main problem is that, when adding a comment, the signature appears in the same line as the textarea that you are writing the content of your post. When you begin typing, your new text actually appears AFTER the signature (at least in Konqueror 3.2).
This makes it incredibly annoying for users because you have to go to the beginning of the textarea before you can type your data.
A corrolary to this problem is that, when quoting (using the quote module), the signature is included by default in the quote, which should not be the default behaviour.
It appears that the signature is being added to the actual body text of the comment, as opposed to being retrieved from the user's profile when the page is rendered.
From an engineering/design perspective, one possible way to fix this is instead of adding the signature text to the comment, instead retrieve the signature dynamically from the user's profile when the page is rendered. If you do this, not only do you avoid the above problems, but you also improve the flexibility of signatures (for example, changing it once will cause the signature to change in every comment you make). You can also use this design change to give the users a choice of when to display their signature (for example, by using a checkbox on the node that says, "Display your signature with this post").