This means the group must be in single formation, all riders follow the same signal.
This means STAGGARED formation.
The OK sign given by the left hand is usually used in OVERTAKING. The first rider gives this to mean that the road is clear for an overtake by the bikes behind him, but not necessarily clear for all of them.
Other signals are given by extending the foot to the direction of a HAZARD. International sign of a HAZARD is by tapping your helmet.
In group rides, specially if you are riding with LERAP, when the BIKE in front does a Z or an S with his bike, the biker following MUST do the same. The “S” is when you drive your bike forming an “S”. This is usually done to warm up the tires.