G-23. Any race
can be stopped at the sole discretion of
the Clerk of the Course by waving the Red flag at the
Start/Finish line. Competitors will be warned that the
race has been stopped by the simultaneous waving of
the Red flag at all Flag Marshalling Posts.

G-80
Red Flag: Immediately Cease Driving at Racing Speed and
Proceed Slowly, Without Overtaking, and With Maximum Caution to Pits or
Startline
Obeying Marshal's Instructions, and Being Prepared to Stop Should the Track Be
Blocked
Hooray!! the Blue Book is absolutely right, the rules couldn't be clearer
(it's probably still in it's original format)
We need to be quick and clear with the Red Flag, however there
are a few ground rules and a couple of tips.
The Red Flag is instigated on the Startline and travels around the circuit in
both directions. This may also be supplemented by red lights. Pick up the red
from wherever you see it, you don't have to wait for the next post (they may be
asleep!), or you may see the red lights. When you have picked it up make sure
the adjacent posts see your signal and give a clear
signal to the drivers.
A word of warning, ONLY show the Red Flag when you have seen either another post
displaying it, or red lights.
Never from a radio or the commentator by all means use these as an
indication that a red is imminent and prepare yourself, I always do a
"double take" just to make absolutely certain that the red is actually
out, as I couldn't stand the
embarrassment factor of an error.
(who was it that stopped a race by briefly leaning on the red light button in a
race control room?)