Myth or not, I too love the story. It's very similar though to days of the past when hobos (vagrants, transients) would mark houses in small towns that were friendly. They would mark at the railroad crossings such as ll>lll^ which would mean 2nd street go left 3rd house on north side of street. I know this because when I grew up in a small town in Northern Indiana along the tracks a vagrant was caught illegally entering a house. He said the house was marked as friendly. He also stated there was no mark stating he had to knock. no wonder he met an older gal with a 30-06. LOL! Have to also remember back in the days of the underground railroad very few slaves could read and therefore had to relay on different signals. I'm still going to believe it to be non-fiction.