Instruction for how to set up a signature or avatar on these boards can be found here. (The "everything" FAQ can be found here.)
It appears that sigs take a little time to get in the system and only apply to posts that you make after your sig is in, and do not come up on previous posts.
VB lets you apply it to all messeges before if you find the little check box, where ever they hid it.
A more comprehensive instruction than is included in the FAQ: 1) In your user cp, Go into 'edit options', scroll all the way to the bottom, miscellaneous options. If it says 'basic editing' change that to 'full WYSIWYG' save change. 2) Next go to 'edit signature' enter the url or if you'd rather you can browse and upload from your pc (options 1 and 2 pictured below). Then in the panel above, where your signature appears, click on the link 'insert signature picture' . Save and exit.