not sure if you have figured this out yet or not but ..

add you signature to photobucket or similar ..

open and log into the furum and click user details (top right)

click Edit Profile  (blue writing in top right above all the details)

There is a box which say 'Signature' next to it on the left... that where the following needs to go..

Now~

Go to photobucket and underneath you signature there should be aload of writing in 3 different boxes..

Right click on the writing that starts like this [img] and scroll down and click 'select all' (it should all go blue) then right click on the blue writing and click 'copy'

Come back to the forum page and  log in and edit profile etc and in the signature box hold your mouse  cursor over it and right click .. and them click 'paste' and then click 'save changes' at the bottom.

Hope this helps if you still needed the advice