Teva! Go to the UCP, got to Profile, then Edit Signature. Are you looking to use a siggy or pic from another website? I'm sot sure what the dimension requirements are, but just copy and paste the link into the box and make sure that the codes are around it. Like this
I don't have admin capabilities so I can't go into you UCP to see what's going on. The only suggestion I can make is to try another siggy or send a PM to whisper and see if she can fix it.