This image (minus the bloody elbow logo which was added in by BE obviously) comes directly from the ABC MMA Rules Report in 2009.
As submitted by:
Committee Chair Nick Lembo, New Jersey
Jim Erickson, Mille Lacs
Andy Foster, Georgia
Dale Kliparchuk, River Cree
Keith Kizer, Nevada
Josef Mason, Colorado
Mike Mazzulli, Mohegan Sun
Bernie Profato, Ohio
"Illegal Strikes to the Back of the Head- Strikes behind the crown of the head and above the ear are not permissible with in the Mohawk area. Strikes below the top of the ear are not permissible within the nape of the neck area."
There was a minor amendment to the side portion of the photo for clarification:
"The group continued to discuss the permitted striking area on the side and the back of the head. The group accepted the back of the head diagram but asked that the side of the head photo be edited to clarify the permissible striking area. Basically, the group concluded that a strike that touches the ear is permissible. As the diagram shows, strikes are not permissible in the nape of the neck area up until the top of the ears. Above the ears, permissible strikes do not include the Mohawk area from the top of the ears up until the crown of the head. The crown of the head is marked on the attachment and is found where the head begins to curve. "