At first glance, it makes sense to assume that either somebody missed a spot, or that UPS doesn’t paint the tops of their delivery vehicles. – But there’s more to this story!
The tops of some UPS trucks have a translucent skylight to allow drivers to see inside without the cost of electricity. This also allows heat to escape in the summer months!
Source
Damn, I Wish
Reddit User: IJustSoiledMyself