Hobo Symbols

I'm always fascinated with symbols of meaning and I came across a website that shared a collection of Hobo symbols. These are symbols that the 'Riders of the Rails' would use to communicate with each other and help each other out. 

An early form of social networks where symbols connected this fringe group of people. As we use social networks like Twitter we sometimes complain that 140 characters isn't enough but imagine what these Hobos could have shared with that amount of data. 

  Propagation Planning could use more symbols of meaning like this.