If you pay to park your car at a lot or anyplace you have to stick money in a slot, try this sometime.
Buy some fake Money and place it in the slot along with your actual payment. Be sure to use real money to actually pay! Otherwise you are committing a crime. All you really want to do is leave a tip of sorts.
This way you can bring a little humor into the lives of people that mostly get grief because people absolutely hate to pay to park. By dropping a little gift, you breathe a bit of quirkiness into an otherwise dreary life.