49 U.S.C. § 14506 — Identification of vehicles

(a) Restriction on Requirements. No state, state subdivision, interstate agency, or multi-state political agency may pass or enforce any law, rule, regulation, or standard forcing a motor carrier, motor private carrier, freight forwarder, or leasing company to display identification on a commercial motor vehicle (as defined in section 14504a), other than identification the Secretary of Transportation requires under section 390.21 of title 49, Code of Federal Regulations. (b) Exception. Despite subsection (a), a state can still require display of credentials needed: (1) under the International Registration Plan under section 31704; (2) under the International Fuel Tax Agreement under section 31705, or under an applicable state law if, on October 1, 2006, the state had a form of highway-use taxation not covered by that Agreement; (3) under a state law about motor vehicle license plates or other displays the Secretary determines are appropriate; (4) in connection with federal hazardous-materials transportation requirements under section 5103; or (5) in connection with federal vehicle-inspection standards under section 31136.