Black text above an illustration of a man in a red and white striped shirt and polka dot bow tie with a red nose, mustache and doubled eyes
The button pokes fun at alcoholics. The phrase "on the wagon" means (of an alcoholic) abstaining from drinking. It was a popular phrase during the American temperance movement in the early 20th century. The original version of the expression was “on the water wagon” or “on the water cart”, referring to carts used to hose down dusty roads.
For more information and the etymology of the phrase: http://www.worldwidewords.org/qa/qa-wag1.htm