In theory, this is a good idea. However, no one believes soda is healthy. We don't need a sticker for that. Yet it sells, and sells, and sells. In general, sans food desert, most of the public has access to healthy options and consistently goes for snacks and goodies.
Sugar and carbs taste good. Irresistible for many. They're also generally less expensive. I'm not sure how a sticker is going to change that.
Pizza was a vegetable in the US, right?
Pizza with enough tomato sauce counts as one serving of vegetable, yes.
You can do a lot worse than pizza, and unfortunately most do. Unless they're getting sugar added as a topping, relatively pizza is fairly healthy.