Tested a signature pic myself. It works, but you have to:
1. upload a signature pic.
2. press the button that says "insert signature picture"
3. save your signature.

Miss any of those and it doesn't work.

Also, it doesn't appear to apply to older posts, just ones you make after uploading the picture. I can run a sql query that will apply it old posts once you get one set up though. Just let me know.

Update: Closing thread...appears these issues are fixed.