I like the "thou shall" better than "thou shall not". Timebandit has the right idea. Let 'em have fun and yell at the machines.

One of the big reasons I got into pinball is that it's something everyone can enjoy. I love it when friends of my kids play because that is probably the only time they have seen a pinball machine. Adults get excited because they have not seen one in decades. Little kids go nuts with all the lights, sound, and mechanical action. Smudges are easy to clean and the machines were built for abuse.