Fund a seed of visible wearers — athletes, public figures, anyone with an audience — to wear the War on Disease shirt on Earth Optimization Day, triggering the cascade where everyone else writes the message on a shirt they already own for the cost of a marker.
The seed pays about a million visible wearers; the grassroots cascade after it costs the world about $0.50 of ink per person. Math: the funniest joke in the universe.