Yes, Mark was a stamp collector. His specialty was air mail covers. A 1931 article in the papers tells of his passion for these covers. He would watch for a new air mail route to open and ask for covers from each town on the route. It reports he also had covers from a Lindbergh Memorial flight and from Admiral Byrd’s camp. It also says that he has an 1847 stamp, reported to be the 1st stamp the US made.
There is a picture of Mark in the 03-18-1928 Decatur Review. The picture is to contrasty for good electronic copying. We think that the paper located at http://www.herald-review.com/http://www.herald-review.com/ is the successor paper.
You might write them and see if they have a copy of the picture.