Sure, Tact. Unfortunately uploading the files for sigs and stuff here is cost prohibitive. Plus, it would slow down load time considerably since it would all be coming from the same server. That's why there is no option to do so.
If you would like to include an image in your signature (or in a post), you first need to upload the file to a space from which you can hotlink it to show up here. AOL has hotlinkable space, as do a few of the file storage sites you can sign up for. If they're still taking new members, hostmysig.com is also an option. Once you have your file uploaded, simply go to your edit signature page and enter the URL of the image inside [brackets] with IMG before and /IMG after the address. Hit save and you should be set.
To include an image in a regular post, do the same thing. Only put the URL in the text space provided when you hit the IMG button that appears in the posting screen. It will appear in just that post.
Hope this helps! 😉
Ann