I was under the impression -- and have probably stated it as something akin to fact -- that marble vending machines weren't specially marked as being for marbles.
I knew that in the 1940's and later, ads were run for vending machines suitable for marbles. It looked like they were pushing a new idea -- to try to keep their machines full during wartime shortages of sugar and ball gum, but I thought those were multipurpose machines, for gum or marbles or whatever.
In 1929, though, they actually had machines specially marked for marbles.
http://aa.arcade-museum.com/Automatic-Age-1929-09/Automatic-Age-1929-09-051.pdf