I've done that myself..... many times.
I've never left a note, I just leave the lid up for everyone to marvel at my creation. They actually got mad at me at work for doing that once. Those girls in the office have no appreciation for true art.
My wife didn't either. *****!
I went to a McDonald's to use the facilities once (because they are typically cleaner than construction site port-o-lets) and went about my business. When i tried to flush nothing happened. When I tried to wash my hands no water there either. Apparently the gardner or whoever was using a hose somehow turned off the water in the men's room, and didn't put up a note or anything. So I left a surprise for whoever went in after me.