All commercial motor vehicles should undergo a DOT inspection at least once a year. If the vehicle in question is a combination vehicle, each part of the chain requires its own inspection. The purpose of the inspection is to ensure that commercial vehicles live up to state standards.
After the vehicle is inspected, it receives documentation of its passing status in an inspection report as well as a decal or sticker that marks the car as passing the inspection. Motor carriers are allowed to perform their own inspections if the car is with the carrier but is not ready for an inspection.