Maybe go back and read again - Issue 11, p 49 states: "All NSW police cars, either for General Duties or Special Traffic Patrol (STP), carried a rectangular illuminated "POLICE" sign that could be shown to a driver, or placed on the rear parcel shelf."

Winabbey's research has since shown that they could also be hung on the side window of a wind-up window Mini - such as Cooper S.

This would appear to be a genuine item, is exactly as described in the research I have found and as shown by Doug's post, but these were apparently common to all NSW Police unmarked cars and all police Minis.

Cheers,
Watto.