Via advertising-hints tweets (here & he got it from groundswellblog), I found a call to stencil with mud.
Yes, Mud. There's even a blog dedicated to it :Mudstencils - where you can pick up tips on how to create the best mud.
Once I had fought off the urge to scream "damn hippies", I soon realized this is the ultimate media for Wisk worldwide. Brilliant! Dirt is good! Keep your eyes peeled for a mud stencil ad near you soon.