Go to the BV home page, and just left of the envelopes for the PM system is symbols of a little man, and another next to that one. Those get you into your account, each has different headings when you put the curser on the icon. You should find how to change things like signatures in that area of your account.
Only thing you can not do is have a signature that holds a personal attack, that follows you anyplace you post. Forinstance if I signed off everytime at the bottom, something personal or direct to you, or about you, etc. Sorry!