I've considered getting a UPN account, but I don't really want another account. Anyway that makes sense (using red type). Maybe I'll start using blue font. It would be fun, I think.
Okay, it's a little confusing, but you have to get the link directly to the post. You can search the post, but I think the easiest way to do it is to:
1) Go to the post that you want to link
2) Click "Edit Post"
3) Click "Go Advanced"
4) Click "Save Changes" (I don't think you have to make any changes)
5) Now once you have clicked "Save Changes" it will redirect you to the thread that the post is on. But now in the address bar at the top of your browser the HTML link will be longer (because it will be for your specific post). Copy this link.
6) Go to Settings, and use the link that you copied as a Hyperlink in your signature
That should work, if it doesn't let me know!