States that genuinely require a suffix
- Montana — intrastate USDOT numbers must be immediately followed by "MT" (ARM 18.8.1502).
- Missouri — intrastate-only authority adds "MO" after the number (7 CSR 265-10.025).
- Oklahoma — intrastate-only carriers add "OK" (OAC 165:30-3-17).
- Wyoming — WYDOT-issued intrastate numbers read "USDOT 123456 WY" (WYDOT Motor Carrier rules).
The folklore suffixes
You'll find decal vendors selling "USDOT 123456 KS" or "... CT" formats. When we verified the primary sources, neither Kansas nor Connecticut requires a suffix in any current statute or regulation — the real requirement in both is the federal format: legal name + USDOT number. A suffix won't get you a ticket, but it isn't the law, and vendors charging extra to "add your state code" are selling a convention, not a requirement.
What every state agrees on
Suffix or not, the marking itself follows 49 CFR 390.21: both sides of the power unit, sharply contrasting color, readable from 50 feet in daylight. We cut 2-inch letters as the practical floor so an inspector never has to squint.
Get it cut right
Order USDOT number decals and put your state in the notes — if your state takes a suffix, we set it correctly on your proof before we cut.
General information, not legal advice. Rules change — confirm current federal and state requirements with the FMCSA and your state agency before you operate. Our state summaries were verified against primary sources July 2026.
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