I suppose if there are enough cars, and if you have access to the wifi and location data for enough of the phones, it might be possible to determine someone's relative location by triangulating the signal strength from multiple vantage points.

So my phone by itself doesn't know the direction of the signal, but two or more other phones could combine our location data with relative wifi signal strength and potentially get a better idea of where the signal is coming from. (I had forgotten that we were talking about an entity that potentially knows the data from all the devices, not just one endpoint.)