in UBB 5, when you selected to post your signature with your post, it became integrated as a part of the post (in the rest of the text, and if you editted a post, you could change the sig).
in UBB 6, the sig is a seperate entity from the post, and is displayed after every post that has the "show sig" flag on. so when you edit a post, you do not see the sig as part of the text of the post, but you can change the "show sig" flag.