1929 4 on 1 postcards

[kmac32]

Enquiring minds want to know. A couple of months back I had won a lot of players from 1929 4 on 1 ESCO post cards with scrapbook residue on their backs. I bought them as an experiment to see if I could soak them and remove the residue. Project was successful with no harm to the players/ cards. With the residue removed on some of the cards in a corner, they have the following inscription:

These coupons have no redemption value in Florida, Idaho, Indiana, Kentucky, Montana, Nevada, Washington, District of Columbia, or any other state in which their use is illegal. Cut coupon on this line. EXHIBIT Chicago USA patent pending

My question is what were these a coupon for? Keep in mind these were postcards.