Click on "Settings" on the top right. On the left of that page towards the bottom is "My settings". From there you can add a sig, change avatar, etc.
Not stupid, man, i already had a signature and had to go thru all the buttons to find where to edit my signature just today. xD
erm.. well now, i dont know where to upload an image to get it in that nice simple URL location, so the sigsaver can locate it
You're right, you are going to sound really stupid... Just kidding, seems like everyone else already got this question covered. Hey, I just got my first post!