i went to go donate and on UM.com's homepage was

no, it's just their ay of saying image linking.

if you turn it off, every image link just shows up as a hyperlink that you have to click to see the image instead of the image just appearing in your post.

In that regard, I believe that if you turn that off, no images will show up in sigs either, just links to them.
 
so it says in the "what you get as a premium member" description..."ability to post attachments".

since you also get webspace (5MB), i'm hazarding a guess it means you don't have to host a doc or image or movie before you put a link up to it; you can just "browse" your computer and post the link and it will upload it into your space?