It does make a great story, doesn't it? But think of all the reasons it WOULDN'T work - travel had to be on a dark, moonless night, so the slaves on foot wouldn't be seen. How on earth could they see a quilt hanging on a fence? If slaves from lots of plantations knew of a code, do you really think slave owners wouldn't? Do you really think the slaves needed a quilt block to tell them to take necessary tools, follow the North Star, or wait until it was safe? I think the story has been disproved, but again, a great story.