I was thinking about this same idea earlier today: Buses in Philadelphia have a bunch of "No Eating and Drinking" signs and consequently no trash cans. The result is that the back of the bus is covered in trash. If they had just 1 or two trash cans it would be a much more pleasant ride.
The people who throw trash on the back of a bus are not the people who would throw that trash in a bin in the bus.
It's not foolproof. There are people who toss trash around regardless. It's a question of making people go out of their way to do something vs allowing them to do it easily.