In the early 1980's, I was working as a Loss Control Engineer for two NC DOT Divisions which consisted of about 1500 employees spread across 11 counties. One of our newly emphasized areas was Fleet Safety & one part of that was the use of safetybelts in vehicles. There wasn't a statewide law nor was it an internal policy but that was what the Fleet Safety program was for.
Anyway, I decided to try a little motivation of my own so at every Safety meeting I spoke at in one Division, I told them that if they were wearing their safebelts during my inspection, they would receive a token of appreciation, a Susan B. Anthony silver dollar. The program seemed to catch on and I gave out quite a few until the funding (mine) ran out. Safetybelt use was higher in that Division than the one without the program.
Several months later, I was walking across one of our Equipment yards when I noted a pickup truck pass by. A minute or two later, it came by heading in the opposite direction and finally turned around and pulled up beside me. The employees rolled down the window and said, "Hey, did you notice that we're wearing our seatbelts?" to which I responded, "Great, that's what I really like to see!" The passenger said, "Well, when do we get our silver dollars?". Both of them were sadly disappointed to learn the program had ended a long time back and the driver remarked, "Damn, I've been wearing this safetbelt for the last 6 months!"
This led, of course, to a pretty good discussion on why it was the "Right" thing to do and they agreed with the reasons why they should do it (and from later observations, they seemed to have developed the habit of wearing it). It also gave me a good picture of how small rewards can affect behaviors.