I believe that the Georgia Sea Island Singers did this in a workshop recently & refered to it as a "code song" & was made up for when Harriet Tubman came around. When Harriet came into the area the slaves would sing a new song to let everyone know her train was coming through, but the songs would change so that no one would put 2 & 2 together. Frankie Quimby claims at least 4 songs she sings are these Harriet Tubman songs. Barry