People who don't believe in the underground railroad and how they communicated don't know what they are talking about.
I am best friends with the great granddaughter of a slave family. And for those of you who are familar of Blind Tom who was a slave and also a famous piano player (debuted on PBS) few years ago was a relative of hers.
I have been bless these last 26 years to have been a part of her history and family, many of whom were slaves, and sharecroppers back in the 18th and 19th century and the things even her mother, herself and families have endured into the 20th century until the 1960's.
Despite what some may think of the underground, or not, just like the holocust some still today will say it never happened and it did.
Slaves in this country communicated messages to each other in manners we would never have thought of to do. Besides some documentation as you find in quilts, and other means they have a wonderful oral history passed down from generation to generation. Todays generation however with all the technology are able to put it all down and have electronic documentation of the history centuries pass to even this day.