USDOT numbers must be displayed on both sides of the truck or cabin of the vehicle. The number must be bold, large (with lettering at least 2 inches high) and legible. For example, if the truck itself is black, the lettering must be in a contrasting color so it’s easily readable.
Most companies choose to place this information on both the driver and passenger doors of their vehicles, and it’s often included alongside other regulatory information, such as an MC/MX number.