You may be confused about the Signature option, and why it isn't working ^.^;;; Well, here are the steps to get it working for ya!!!
1. Go to your Profile, just clicking on the link once.
2. Look for Preferences, and please click on it.
3. You should see a big list of options >.< Yeah, it's in that list.
4. Scroll down until you see: "Always attach my signature"
5. Click "Yes" and save.
Also, in the same area, just below "Always attach my signature", is an "Always use HTML". It wouldn't hurt to turn that on too. ^.^