How many times do I have to answer the same question?
Just answer it once. Hanging a plaque is not enforcement. You said " some ground rules would have to be enforced." A plaque could be ignored like a No Parking sign. That's why cops have to write tickets for parking in No Parking zones even when there is a sign posted. So, how would you prevent churches from simply covering up the plaque? How would you prevent a preacher from standing in the pulpit and saying "In the beginning God created the heavens and the Earth, and that is a fact!" ???
Why would anyone try and prevent a preacher from making a fool of himself?