Rally Argentina is over... Meeke won.

the question is simple...

Is there an official regulation that states what a driver must do if he doesn't see any sos/ok/triangle and gets an incar signal that the car in front is not moving ??

I am aware that if a driver gets a sign he must act accordingly, but so far people are accusing Tanak that he did not slow down/stop while there was no indication for him to do so (apart from a guy standing 10 meters away from the accident)