Do not throw out your garbage?

Okinawan signs continue to baffle me from time to time. We pass this one on the way to karate every week and it caught my eye (and I caught the red light, so I could take a photo). Still unsure exactly what it means, but I am going with not throwing my grabage out. Not sure who the sign is directed at (because at this moment I was parallel to the sign and there was no oncoming traffic in the direction of the sign...), but good to know.