The criminal underworld in Telisar is comprised of several independent, sometimes-aligned, often warring factions separated by geography and areas of concern. But even amongst competitors communication is important, and concealing communications from the city watch, the nobility, the Order of Woden and other such ne’erdowells is crucial. Thus the various thieves guilds and other criminal organizaitons turn to a secret code: Thieves Cant.
In the DMG Thieves’ Cant is described as a “secret mix of dialect, jargon, and code that allows you to hide messages in seemingly normal conversation.” That’s all well and good but not very useful as a mechanic at the table. Since I firmly believe thematic elements need to be manifest in mechanics for them to be relevant to play, I wanted a mechanism the players could actually use. So I turned to one of my enduring inspirations: the Freemasons. The Craft secured their communications using a simple substitution cipher based on the following key:
To use the key, you replace the letter with the corresponding geometric shape: A becomes A, B becomes B, and so on. I learned the masonic cipher as a kid (I was that kind of kid) and the ordering of the grids in the version I remember differs slightly from this example, but the principle is the same.
So anyway at a dramatically convenient moment I had the players discover a few sheaves of parchment encoded with these symbols, which I actually handed out at the end of one session. Naturally my players had it cracked in about an hour (because we are all that kind of kid), and now I could hit them up with short messages, traveller glyphs, etc. in game as a reward for an investigation check, or to lay subtle hints or misdirections as a result of passive perception.
But encoding and decoding is a pain; I don’t use it as much as I would like because I don’t have time to sit down and encode lengthy messages before a game, and decoding anything more than a word or two at the table breaks the flow of the game. Which led me the idea of creating a font for our version of the Thieves’s Cant that I could put on the website, and which the players could decode in real time if they’re quick, or simply toggle the font if they’re going to devote a short rest to decoding a longer message.