Well yay is all I can say.
From the very beginning of using mybb I hated the way the user signature displayed on the classic postbit.
It was sort of like POST CONTENT - underline(only 25% width) and then a load of signature crap......
I hated it - I wanted the signature to be neatly away at the bottom of the post - not being a blob of horror in the middle of the post.
Finally - I have fixed it. What does this show? That if you plod for long enough you will learn how to do the things you want to do