How to tell when your sign isn't working

There are lots of signs that mean well, but don't make sense.

When I see a "Nuclear Free Zone" in a city, I wonder if that city's hospitals are required to abolish their Nuclear Medicine departments and cancel Radionuclide Therapies, such as those that are used in treating Thyroid cancer. 

How about the signs that say "Gun Free Zone?" That sounds good, but how would you enforce that policy when someone shows up with a gun?  Calling someone with a gun to enforce a no gun policy sounds like admitting that guns are needed.