A “hobo” is a migratory worker who wanders from place to place without a home or job. To cope with the uncertainties of hobo life, hobos developed a system of symbols, or a visual code. Hobos would write this code with chalk or coal to provide directions, information, and warnings to others in “the brotherhood”.
Interesting; my Grandmother said she grew up near some railroad tracks and her parents would feed hobo’s when they could. I remember he telling me that her mother asked a hobo how he knew to go to their house for food and he told her their house was “marked”. The guy said something was written on the sidewalk in front of their house which indicated they were friendly people.