Flaggers are the second manifestation of Race Control. Just like the pit marshals on pit lane, the flaggers keep watch, enforce rules, and relay observations from around the track. They communicate with the drivers by way of a set of flags, and they use radio to communicate back and forth with Race Control, and/or with other flag stations.
The flags encode a small set of relatively terse messages, including things like "caution," "faster cars approaching," "dirt or oil on track," and "you did something bad; pit now." The flaggers also use motion to convey urgency — a waving flag is more urgent, a still (or "standing") flag is less urgent. Anything more nuanced will likely come over the radio, once the pit marshals talk to the driver's crew chief.
The flags encode a small set of relatively terse messages, including things like "caution," "faster cars approaching," "dirt or oil on track," and "you did something bad; pit now." The flaggers also use motion to convey urgency — a waving flag is more urgent, a still (or "standing") flag is less urgent. Anything more nuanced will likely come over the radio, once the pit marshals talk to the driver's crew chief.