Retroreflective Sheeting in red and white strips or white strips is required only on trailers and tractors that are regulated by the FMCSA. This material is discussed in the Federal Motor Carrier Safety Standards at 501.108 and states, at S5.7.1.5 Certification. The letters DOT-C2, DOT-C3, or DOT-C4, as appropriate, constituting a certification that the retroreflective sheeting conforms to the requirements of S5.7.1.2, shall appear at least once on the exposed surface of each white or red segment of retroreflective sheeting, and at least once every 300 mm on retroreflective sheeting that is white only. The characters shall be not less than 3 mm high, and shall be permanently stamped, etched, molded, or printed in indelible ink.
This federal requirement does not apply to straight trucks no vans, therefore the certification is not required on the reflective sheeting used on these trucks