> What's the difference between an "unmarked car" and a "nondescript vehicle" ?

Unmarked police cars often have multiple radio antennae, flexible lights, and even government plates, they simply lack explicit police markings and light bars.

Surely an unmarked van owned by Apple would have none of that?

The point is that the "unmarked" vehicle sticks out as unusual even without having "Apple" or "Police" emblazoned on its side.