We received back a form that is digitally signed, but instead of the signer's name, it starts out with zune-tuner://windowsphone . . . with a bunch of following characters. What went wrong with this person's signature, and can this be a valid digital signature? What should we advise the person to do?
You probably need to give them detailed instructions on how to sign with the phone and software they have. This does appear to be a valid certificate, intended for some other use, but quite possibly entirely valid for this purpose - but anonymous. It may be in the phone's certificate store, and available for selection.