Thieves Cant

Thieves' cant (also known as thieves' argot, rogues' cant) is a cant, cryptolect, or argot which is used by thieves, beggars, and hustlers of various kinds.
It's a secret mix of dialect, jargon, and code that allows you to hide messages in seemingly normal conversation. Only another creature that knows thieves' cant understands such messages. It takes four times longer to convey such a message than it does to speak the same idea plainly. In addition, it includes a set of secret signs and symbols used to convey short, simple messages, such as whether an area is dangerous or the territory of a thieves' guild, whether loot is nearby, or whether the people in an area are easy marks or will provide a safe house for thieves on the run.