Thieves' Cant

Thieves' Cant is said to have originated from some master code breaker. A man so gifted in the ways of numbers and letters that he invented entire new symbols, ones that could be hidden in everyday shapes, carvings, drawings, or any other medium really.
This, of course, isn't true. The mechanics of it are correct. The Cant is able to be hidden just as well under the eaves of a seedy bar as it is in the folds of a lady's dress in a fine painting. It is used for many purposes, chiefest of which is communicating a state of danger or safety to various agents making their cautious way through a city.
The real origin of Thieves' Cant is the ancient Zawilian Civilization (See Zawilu for more information). They developed it as a sort of slang. A visual shorthand they could put into their writings, art and crafts that would inform only those in the know of certain properties, information or simply inside jokes. Their ancestors, those who moved away before the great disappearance, spread the use of it to other Caiten clans, and many forgot it, but at some point in history, the Cant was given to those not of the Caiten species and it soon became of chief use for any person working to do secret or perhaps illegal things.