Does a flagger have to wear a vest?
No.
According to the FHWA, as long as the apparel meets ANSI Class II, 107-2004 requirements, the flagger, or any other worker is in compliance with the MUTCD. Flaggers are not required to wear a vest. A shirt, jacket, vest or any other apparel meeting the standard is acceptable. However, a local agency may require that the flagger wear a vest as a local policy.