I do not agree with the answer of the first replier.
1) 係未郵政車有特權在禁區停泊而唔會俾抄牌呢?
No. They should not
2) 係未政府車輛有特權在禁區上落客呢?
No. They do not.
You can send a complain to the Police immediately. They will issue penalty ticket even though Government Vehicles do not need to post up their registration document. Police and Traffic Wardons can still issue penalty tickets by drop down their Card Plate No. (i.e. AM XXXX).