We have a sign that says only pilots on the flightline though I'm not sure if non flyers would know what means. We are also out of the way a bit so we don't get many drive bys. Though the one time we did have a visitor when i was there alone..... out he came past the flightline to the pilot stations we have set up while I was flying and the questions started. So I guess we need some better signage like:

Thank you for visiting today. For your safety, please do not cross the yellow line painted on the ground just past the shelters. If you have questions, please ask anyone NOT currently flying or working in the pit area with a running motor and they will be happy to discuss this wonderful hobby with you. If when you arrive, the only club member present is "flying" an airplane or helicopter, please be patient and wait for the member to land and shut off the motor. Thank you.

This is a bit much.. but then again.. maybe it's not.