The DOT number must be displayed on both sides of the vehicle. There are no specific regulations as to the place, but the door of truck cabs is a popular choice since it provides enough space to put the required information.
The lettering of the USDOT number depends on the background color of the truck. If your truck is white, you should paint the USDOT number in black. If your truck is black, then paint the letters in white. The letters must be readable at a distance of 50 feet from the vehicle when it is stationary. Therefore, you should make sure your letters are not only opposing the background but are also a large enough font to be seen easily.
You need to apply for as well as display a USDOT number on your vehicles if