I think the problem with telling most people not to touch your screen is that often they don't see an alternative. So I always make sure I have a pen with me.

I think the problem with telling most people not to touch your screen is that often they don't see an alternative. So I always make sure I have a pen with me. If someone touches my screen, I usually just hand them my pen and say "Here, point with this". Not only do you avoid the finger-oil issues, but it's also more accurate.