How big of an empty space are you seeing?
You've been unofficially banished, so there is a Banished rank above your official rank. It has pushed everything under it down. If there is any blank space, it is only because all the stuff on the left under your avatar descends lower than your signature. However, if you make a big, lengthy post, that space should go away. It's only short, little posts where the space is more visible.
But let me know if that's not the case. I can look into it further.
Samurai Equine's post in Blank empty signature space was marked as the answer