http://www.smogon.com/forums/account/signature
Try clicking that^ If that doesn't work, I'm stumped.
You are my savior, thank you! I think my account had a strange quirk that was keeping the "signature" menu item hidden, somehow. I haven't logged in to this account for years, and I know the whole forum has switched to a different site-webhost-thing. The quirk/problem was probably caused by porting this old, disused account between services, but when I visited the signature page with the direct link the problem fixed itself and now the menu option is where it should be, matching what Montsegur's screenshots show. *shrug*
Is there a bug report thread? This is definitely a bug, and the programmers might be interested in this happening and my screenshots.
New screenshot featuring signature option now where it should be--->
http://i.imgur.com/N5zwhEN.png
Edit: Is there a limit on forum accounts that requires a certain minimum number of posts before the account's signature can be edited? I know some websites limit certain account functionality like that for new accounts.
This accounts signature was established years ago, but I had never made any forum posts. If a minimum post limit had been imposed between the time this account's signature was added and the theoretical signature restriction then this account would have been barred from having access to the signature option; intending to prevent new and therefor possible spam accounts from creating signatures, but in my case simply barring access to removing or editing the existing signature of my account.