What if a secret society of rogues operated in plain sight, using code words to plot elaborate felonies and hoaxes? From the 16th to 19th centuries, Europeans believed exactly that. According to multiple authors, rogues spoke a secret dialect called thieves' cant, which even the police couldn't crack. Honest folks needed to learn the language quickly so they could avoid "priggers" and "badgers" - known in standard English as thieves and villains.