Good job!
If you want to change peoples' behavior it's better to praise them for doing right rather than punish them for doing wrong. Especially when "wrong" isn't clearly accepted as such.
Here's a counter built into a drinking fountain that shows how many plastic bottles weren't needed because people used the water fountain. Oops, I mean H20 Station.
Have you seen other examples of positive reinforcement recently? If so, please talk about them by clicking "Comments" below.