Hmm - it is easy enough to add a signature (under "Community Settings" under your forum name in the right margin), but the "save" button for the Community Settings page won't remove the signature again if you later delete everything in the signature box and click save.
It will save a visually empty signature if you make a signature consisting of just one space, though. A small bug there :-)
Grin, Stein
Testing to see if a new reply to a thread will make the thread visible again as unread after marking all threads in forum as read.
/S