One of my players is playing a mouse assassin. Over the course of the game he's developed a mouse "culture" -- mice are small, nobody really pays much attention to them, and they're relatively weak, so they have a sort of network to keep them informed of what's going on. If you've ever read the book "Spook Country" by William Gibson, they're the Systema, a group run by "uncles" that tries its best not to be noticed.

He has developed what he calls the "Whisper Tongue", which is a written code the mice use when they need to communicate. It's based on the suns and moons and only has a few symbols. I gave him some help with the linguistics, and it pretty much works! We tried sending a few messages in it and though it may evolve over time, it does what we need it to do. Now I can send him in-game messages that everyone else will wonder about.

Here's the link:

obsidianportal.com/campaign/wh…hisper-tongue-of-the-mice