Urban Farm Magazine has an instruction and comical video explaining how to make seed bombs that can be used to seed brown areas in the city. All undercover of course. As shown in the video, after the seed balls are made, you can run around town and slyly infuse different yards and unproductive areas with your seed bombs.
One benefit of the seed bomb is that the seeds are provided with nutrients from the worm compost while the clay holds everything together. This way the seeds have a better chance of survival once they hit the ground.