[aerohead]

If you'll tail the truck during the rain event, you'll witness a horizontal geyser exploding out each side of the truck. At the rears as well.
The soiled water has much higher density than the air in the same area, and indicates telltales a little different than what the air would.
Capillary action allows the watermark some contiguous streaking which would also not be present in the airstream.
Analyzing the reattachment point behind the emblems, based upon their thickness would be qualitatively instructive.