That is exactly why I don't send certified mail. Most people refuse to sign it. If some one does sign for it other than the addressee, it does not stand up in court. There is always the chance that the one who signed for it, did not pass it on to the addressee.
I use a tracking number only. For Pay or Quit notices, I post and mail it with a tracking number. First class mail is deemed delivered in court. With a tracking number it is verified.