A friend of mine is, on occasion, required to transport ‘high value’ loads.
The Police have advised, unofficially, not to stop for ‘ANY ’ vehicle other than an officially marked patrol car.
As stated before, because these light kits are available for any muppet to put on his vehicle and when hidden in a radiator grille, are not easy to spot when not turned on.
There has been a spate of high value loads / prestige cars / exotic motorcycles, being targeted by thieves.
They will stop a vehicle, request the driver to follow them, for the vehicle to be spot checked by the ministry of transport. They will have people waiting for them when they get there, the driver will then be bundled into another vehicle and taken out of the area and dropped off in the middle of nowhere, minus phone etc.
With trucks, sometimes they will put the driver into the dodgy police vehicle and take him straight to a drop off point, while another ‘officer’ drives his truck in the opposite direction.
The Police have said that this is becoming more and more of a problem, having accounts of trucks & loads disappearing for weeks, high performance/classic cars and bikes vanishing, never to be seen again. Bikes can be more desirable than cars in some cases as they are easier to transport in a van and the market abroad is not affected by left/right hand drive.
I would be less likely to stop for an un-marked police car, if in my view there was no reason for the pull.
Especially if I was riding this:
"If it's not broken, fix it 'till it is - If your not sure how it works, take it apart and find out - If it don't work when you put it back together.......look in the manual"
Theres several home pages on my puter and its not just me that uses it. 
Zero tolerance policy! 