The backwards writing on the side of the truck was a small puzzle. Why would the numbers — and a series of vertical letters — be written backwards? Then I actually read them and it immediately became apparent: “15′ 1″ HIGH.” It’s the truck’s clearance, written so the driver or his partner can read it on the side view mirror. Any time they come upon a posted Low Clearance sign they can easily compare it to the truck’s requirements. Rather clever actually.