Who's trucks are these?

Early Friday morning, 4:00 AM to be exact, we all got up to take Vicky to Metro Airport to catch a plane to Florida to see Leeta, her big sister. Both on the way to the airport and on the way back, we saw a heck of a lot of trucks on I-94. Most of the trucks proudly proclaimed their owners; Kroger's, Beacon Movers, Ford Motor Co, etc., but many were absolutely unidentified. I have noted this during many trips in recent years. Big white semi-trailer trucks, not a word, not a number, not a picture anywhere on the trailers or the trucks, the only identification showing at all being the license plate, if that isn't covered in dirt. I find them troubling, especially with terrorist attacks a real possibility in today's world. What are they carrying? Where are they going? Where did they come from? Who owns them? Even if these are leased or rented trucks, why wouldn't the owner want to at least have a discreet sign saying something like, 'Bob's Big Truck and Trailer Rental' somewhere on the trailer and truck? And if one of these semi-trailer trucks is ever stolen, what description do you give to the authorities? 'Ah--- its white, and it's big'. If the thief changes license plates, I would think, you might never see your truck again. I think there should be a law requiring some kind of identification on commercial vehicles. I am sure no one ever would have thought there would need to be such a requirement, as in the past, owners were only happy to advertise themselves on the sides of their trucks, which is why I find these totally blank trucks puzzling and ominous.