Actually, although they don't enforce it along the waterline, you are are required to have a flag on all vehicles if you venture out into the bowls. If anything do it for safety's sake. Remember your sharing those dune's with kids on quads who might not see you when there coming up the face of a dune, untill its too late..
EQUIPMENT
All vehicles operating in the SVRA (beach and dune area south of Post 2), must be equipped with the following:
An adequate muffler. (Required for vehicle operation in any area.)
An 8' whip with an orange or red flag with a minimum size of 6" x 12".
Except for two-, three-, and four-wheeled cycles, all vehicles shall be equipped with adequate roll bars or roof structures of sufficient strength to support the weight of the vehicle and shall have a secure seat and seat belt for the vehicle operator and each passenger. Seat belts shall be as specified in the California Vehicle Code.

EQUIPMENT
All vehicles operating in the SVRA (beach and dune area south of Post 2), must be equipped with the following:
An adequate muffler. (Required for vehicle operation in any area.)
An 8' whip with an orange or red flag with a minimum size of 6" x 12".
Except for two-, three-, and four-wheeled cycles, all vehicles shall be equipped with adequate roll bars or roof structures of sufficient strength to support the weight of the vehicle and shall have a secure seat and seat belt for the vehicle operator and each passenger. Seat belts shall be as specified in the California Vehicle Code.