FIA Rules
4.1.2 Flag signals to be used at observation posts:
a) Red flag: This should be shown waved only on instruction from the Clerk of the Course when it becomes necessary to stop a practice session or the race. All drivers are required to slow down immediately and proceed to the pit lane (or the place foreseen by the regulations of the Event), and must be prepared to stop if necessary. Overtaking is not permitted.
b) Yellow flag: This is a signal of danger and should be shown to drivers in two ways with the following meanings: – Single waved: Reduce your speed, do not overtake and be prepared to change direction. There is a hazard beside or partly on the track. – Double waved: Reduce your speed, do not overtake and be prepared to change direction or stop. There is a hazard wholly or partly blocking the track. Yellow flags should normally be shown only at the marshals post immediately preceding the hazard. In some cases however the Clerk of the Course may order them to be shown at more than one marshals post preceding an incident. Overtaking is not permitted between the first yellow flag and the green flag displayed after the incident. Yellow flags should not be shown in the pit lane unless there is an incident of which the driver should be made aware.
c) Yellow flag with red stripes: This should be shown motionless to inform drivers that there is a deterioration of adhesion due to oil or water on the track in the area beyond the flag. This flag should be displayed, for at least (depending on the circumstances) 4 laps unless the surface returns to normal beforehand. It is not however necessary for the sector beyond where this flag is being shown to show a green flag.
d) Light Blue flag: This should normally be waved, as an indication to a driver that he is about to be overtaken. It has different meanings during practice and the race. At all times : – A stationary flag should be displayed to a driver leaving the pits if traffic is approaching on the track. During practice : – Give way to a faster car which is about to overtake you. During the race : – The flag should normally be shown to a car about to be lapped and, when shown, the driver concerned must allow the following car to pass at the earliest opportunity.
e) White flag: This flag should be waved and is used to indicate to the driver that there is a much slower vehicle on the sector of track controlled by that flag point.