Saw this one today near Route 28. Silver four door Dodge Charger with three small antenna: one black plastic cylindrical on trunk, one black plastic swoop on rear window, one black wire on rear window. Hanging from passenger's side door on window inside passenger compartment were what looked like emergency lights.
Plate read "T1DKID" with the Virginia Railway Heritage plate:
http://4.bp.blogspot.com/-CyS5Z6aaNuU/UjhTsGPGCbI/AAAAAAAAAdk/mIwGSElUErQ/s1600/va-plates-railway.gif
The more I think about it, possible railway official, though I originally thought unmarked PD? Not sure.
I'd post picture if I could.