Why does Willie Bester paint pictures of poor people and frame it on stop signs?

There is no known artist named "Willie Bester" who paints pictures of poor people and frames them on stop signs. This appears to be a fictional scenario.

It's possible you've encountered this idea in a work of fiction, a dream, or perhaps misremembered a real artist.

If you can provide more context about where you encountered this idea, I may be able to give you a more specific answer.