I have mixed feelings about Colibri's first post.
On one level, challenging and identifying people who are round and about our airfields seems extremely sensible. On another level, it is acting in a somewhat hostile and suspicious manner towards people who traditionally we'd just freely chat to.
I think that if going down this route it's probably wise to put up warning signs along the lines of "welcome to XXX airfield, visitors may be asked to identify themselves and show photo ID", if only so that the sign can be pointed at.
One thought - I'm in a small group with two friends operating a 912 engined microlight on a farmstrip. A few months ago we changed our name on G-INFO from "(Airfield name) (Microlight type) syndicate" to "(Registration) (Microlight type) syndicate" so that the location of the aeroplane isn't so obvious. Also - if you have a member with a home address right next to the airfield - don't use them as the trustee, as their address will appear on G-INFO and gives too heavy a clue as to the aircraft's location also.
G