Hi Chris! I just got what you're seeing as a problem, I think, but it's not actually anything isn't working right. It's just how edit sigs works.
For an image sig, you need to click IMG in the list of BbCodes first, and you'll get a popup window asking you for the URL of the image. If you add it there, then when it's inserted into the box, it will display properly. If someone cancels that popup prompt though, you will get the IMG tags in the box but it will say Null where the URL should be. If you'd already put the image url in the box first, then yes those tags would be after instead of around.
Same thing for text. If you want a text sig, with an effect, like maybe Glow, you need to click the code for the effect you want first. The tags will be inserted into the post and then you need to actually insert your text between the opening and closing tags. If you type your text first, highlight it and try to get the tags to surround it, it won't do that. It will put the tags at the end of the text, but that's normal for edit sigs and not an issue or anything ya'll are doing wrong.
Hope this helps a little