I was stumped myself a couple of days ago. Click my banner and it takes you to the page that makes it for you, copy the BB code. Now add the copied code as your signature and he presto.
If you want a banner like mine, go here: http://www.puffin-eliquid.com/ukv/
input your info and choose background and click generate banner.
you will see a image of what your banner will look like, below that will be a box with some code in it that will look like thiswith [ ] around parts of it)
url=http://www.puffin-eliquid.com/ukv/
img http://www.puffin-eliquid.com/ukv/?banner=3180 /img
/url