Spies used to make their secret markings with chalk, but rain has always been an issue. Here in the Bay Area it can rain for weeks on end in the winter, so chalk is really out of the question. Now that the Cold War is starting up again, there is increasing spy activity. Innovations in the spy industry never cease. Here, you can see modern spy markings in fluorescent spray paint. What they mean is a mystery. I suspect they have something to do with sexual geography. The shapes are quite voluptuous.