I see signs in southern Ontario saying "Your Are Now Entering the Greenbelt"?

I'm sorry, but your question cracked me up so bad! I just had to say thanks for the LOLZ!

Oh something far more sinister. It's an area of land protected because it's prime farmland and excellent green areas for people in the province:

"Ontario's Greenbelt is a world-leading law that preserves prime farmland and green spaces around the Greater Golden Horseshoe and is vital to the quality of life of Ontario. The Greenbelt's 1.8 million acres (728,000 hectares) encompasses the Niagara Escarpment, the Oak Ridges Moraine, Rouge Park, agricultural land, pristine forests, wetlands and watersheds, and hundreds of rural towns and villages. It gives us clean water and healthy local food. It's bigger than P.E.I. and, in fact, is the largest Greenbelt in the world. "