Here is a Marquard letter of mine. Also, regarding Jeff's theory, I think that it is likely spot on, although I had a very tough Marquard signed 1979 Grand Slam card that was somehow authenticated by JSA although it was very much an end of life type of autograph. So there may have been days where he did sign things that were sent to him through the mail instead of just generic 3x5's and photos.
Tom C