Cracking the hobo code

Came across a book, 'Symbol source book' by Dreyfus, which illustrates some of the symbols used by hobos to communicate with each other. I wonder if there is a syntax involved in combining different symbols. Or is there a guideline to where these symbols get displayed, perhaps high traffic areas or points of conversion and switching within the railway track system. perhaps there is a connection with the symbol locations and the location of actual switch, drop/ pick up points along the railway infrastructure. I see the symbols as an opportunity to develop a program: a narrative to be tapped into , they may be real or fictitious. The simplicity in the 'pictorial language' of the drifter, one who is free to go where they want but is still bound by the confines of the infrastructure available to them.