What a cool idea to use moss as graffiti, to grow it into words or a design! Can you imagine if all spray paint graffiti was replaced with "green" graffiti? Reminds me of Seed Bombing. Anyway, so Crafting a Green World has a great tutorial on how to make your own moss graffiti. Essentially- in a blender add one can of cheap beer or 1/2 cup of buttermilk, add a few handfuls of moss, and one teaspoon of sugar. Blend it together and then paint in on a wall and mist daily until it grows! I think this would be fun for a party, wedding reception, used at a garden store (I'm looking at you Terrain!), or at a little cafe. If you try this, let me know how it works!