Most "station masters" and "conductors" - the people involved in the UGRR- only knew the next station and sometimes the one before them. The less one person knew about others the more protected everyone was. Obviously signals were worked out to allow conductors to know if it was safe to bring their passengers into the "station". It might have been something hanging in a certain spot, or a specific color etc. quilts, as well as other items might have been used. This may be where the story began, and the myth grew over time.