I dreamt about this last night. I read about it in Anthony Shafton's book Dream-Singers, a few weeks ago. He describes how African Americans use dreams for numbers gambling. Although they may do it less than they used to. What I found interesting is that it only works with dreams of others. Which means that gambling motivates people to share dreams. They may not be much interested in the dreams themselves, but it still helps to create a setting in which dream sharing becomes common.
I've heard that Italians do the same. I tried to learn more about it, but I don't know that many Italians. Do Italians need dreams of others as well? And, if African Americans and Italians use dreams for gambling, couldn't there be many more people who do this?