The Underground Railroad:

Most members of the underground railroad system were uneducated, so it was hard to send messages securely without getting caught. So, they communicated through pictures - pictures on quilts. This code was understood by every passenger through days of training before heading for the road. Finding the right way of communication is necessary for a successful operation: it had to be understandable by every member, but not The System of the Underground Railroad is one of the greatest examples of the theme Communication in History: The Key to Understanding.