Washing hands?
Do you happen to know if that (old) story about alcoholics nicking the handwash had any truth?
In any case - its the punters who need a good slap. It's in front of them on entering a ward. Typically it's positioned so their face is right in it, to open the door, yet some people don't.
I'd have a camera there and post them up on a large screen to embarrass them. You'd only have to do it a few times then all you'd need is the sign.