A formation will be deemed genuine if:
1. you are not caught making it.
2. the pattern represents a shape which leading cerealogists could regard as of symbolic importance, and, therefore, useful on the proselyting lecture circuit, e.g. mandalas, Atlantean script, etc.
Of course, it might just be that crop circles are made by the bored controllers of secret satellites (and who also occasionally shoot down aeroplanes just for the heck of it) that only this guy knows about. But it's unlikely.
Going Around in Credulous Circles 3
Going Around in Credulous Circles 2
Going Around in Credulous Circles 1