Well, once I saw that you had originally set a length restriction of one character in an attempt to thwart the spambots, I didn't attempt to edit my signature block code. I could see that, as soon as I brought up the edit-profile page, the text in the signature code edit box was replaced by a single "[", so I simply backed out of the page.
When I saw today that you had lifted the restriction, I again brought up the edit-profile page, saw that the text in the signature code edit box was staying as it previously was, so I felt confident to edit it -- so, I only noticed the problem today.
(By the way, you'll have seen a request from me for a second account. Nothing sinister intended -- I was just going to test whether the problem is peculiar to my present account, and then delete the second account.)