Scroll to the top of this page. Near the left side click on User CP. On the next page along the left side you'll see the column headed Your Control Panel. Scroll down and you'll see the option to Edit Signature. Click on that and it'll bring up the screen to edit your info.
Yes go to forum main page, click on user CP. Click on "Edit Signature: Choices for all will look like this:
Your Control Panel
Your Profile
Edit Your Details
Profile Privacy
Edit Profile Picture
Networking
Contacts & Friends
Social Groups
Pictures & Albums
Settings & Options
Edit Avatar
Edit Signature
Edit Email & Password
Edit Options
Edit Ignore List
Edit Your Canned Replies
Private Messages
List Messages
Send New Message
Track Messages
Edit Folders
Subscribe