If you run a commercial vehicle in interstate commerce, the Federal Motor Carrier Safety Administration (FMCSA) requires your US DOT number to be displayed on both sides of the power unit. Get it wrong and you risk fines at a roadside inspection — get it right once and you never think about it again.
One note on the citation, because it trips people up when they go looking for the rule themselves. Everyone calls this "390.21," and in conversation that is fine — but section 390.21 was suspended when FMCSA paused its Unified Registration System rollout, and the text actually in force is section 390.21T. The requirements are the same either way; FMCSA even titles its own guidance "Marking of CMVs and Intermodal Equipment (390.21T)." If you pull up 390.21 on eCFR and find it marked suspended, that is why, and 390.21T is the section you want.
What has to be on the truck
- Your legal business name (or DBA name as registered with FMCSA).
- The letters "USDOT" followed by your number.
- Your MC number, if you operate as a for-hire carrier crossing state lines.
Size and legibility rules
The markings must be in a color that contrasts sharply with the background, be readable from 50 feet away in daylight, and stay legible for the life of the marking. In practice that means clean, high-contrast vinyl lettering — not a faded magnet that peels at highway speed.
Permanent vinyl vs. magnetic
FMCSA allows removable markings, so magnetics are legal. But for a vehicle that lives on the interstate, permanent cut-vinyl lettering is the safer call: it will not blow off, slide, or trap moisture against your paint. We cut both — tell us how the truck is used and we will point you to the right one.
Bring us your USDOT and MC numbers and we will lay out a compliant, sharp-looking set the same day in most cases.