Making signatures can be done a ton of different ways. Usually people use photoshop or gimp, or crop a simple picture down to the required height and width (Max of 250x700.) From there the image is uploaded to a photo hosting service (Imgur, Photobucket, tinypic) and entered into the signature box from the top of the screen. Settings > Edit signature with the tag
You should be able to find some tutorials around the site in the museum.
If you close a thread, you can't reopen it yourself and most of the time unless it's AC related, you can't close threads. Report the thread and it'll be dealt with. It's a button with a triangle and exclamation point below your post in the tan bar.
I don't remember how long you can edit titles for. It should all be under the icon that says edit post with the pencil in the tan bar under your post.
~You can only open and close your threads in ReTail, Villager Trading Plaza, and the TBT Marketplace. You can do this by clicking the "Administrative" tab on the toolbar at the top of the thread.
~You can click "Edit post" underneath your post, and you can click "Go Advanced" if you want to edit the title or other things such as the text alignment. Alternatively, you can double-click on the thread's title to edit it.
