Laundry Room Issues

I have a 4-plex with one coin operated washer and dryer in the common area. Since a new tenant moved in, we have had other tenants complain about clothes being left in the washer and dryer for days at a time. To me, it would be common sense that if you put clothes in a machine, you would come back an hour later and retrieve them...apparently this is not the case.

How should I handle the situation? I have thought about two methods: to either post a note in the laundry room or to send a letter to each of the tenants. Which method would you recommend? What should either the note or the letter read? Thanks for the advice.