Thieves' Cant

The Thieves' Cant, also known as the Rogue's cant or peddler's French, was a secret language formerly used by thieves, beggars and hustlers in Great Britain and other English-speaking countries. The classic, colourful argot is now mostly obsolete, and is largely relegated to the realm of literature and fantasy role-playing, although individual terms continue to be used in the criminal subcultures of both Britain and the U.S.

A few resources for the player who may wish to learn more about this argot, perhaps to even use it within the game, should check out the following links:

http://www.thievesguild.cc/thieves-cant

https://owlcation.com/humanities/All-things-HOBO-signs-and-symbols