I meant between WWI and II. I wasn't aware of the earlier movement. I first became aware of it watching the 1936 film version of The Petrified Forest, which features anti-tipping as a minor background element, and has a contemporary (to its release) setting—the play it's based on was published in 1934.
As I understand it, you were seeing the last vestige of the anti-tipping movement (just based on the timeline) in the movie. A few states even had anti-tipping laws before WWI that disappeared during the 20s.
