Landing Area Circle Marker

[Slainte]

I am trying to track down the history of the large white circle seen in old airfield photos. US Forest Service strips have them still.
I understand that it was used to designate a 'field', that looked like any other farmer's field, as a designated air-field. I have seen a reference to the September 1932 "Airway Bulletin No.1 'General Airway Information'" publication. I have seen portions of the manual at oldbeacon.com. but they don't satisfy my curiosity.
Does anyone have a copy of this government pub?

[Noyade]

Can't help mate, but I saw this in a book last year. Somehow related?

http://img442.imageshack.us/img442/1825/cropcircles.jpg (http://img442.imageshack.us/i/cropcircles.jpg/)

[chevvron]

Over here, the white circle usually contained the airfield name, plus a smoke source to give wind direction (usually an open tank with a slow burning oil)