One problem with signs is that people don't read them or comprehend them at any altitude.
As for people who are bone-tired, or those even truly mildly hypoxic on a moderate altitude peak like Whitney, or those rare persons who actually have early HACE, is that they can't recognize the situation. The observant quote below (from the most famous Everest climber) is not meant to be an insult:
Mountaineers have often observed a lack of clarity in their mental state at high altitudes; it is difficult for the stupid mind to observe how stupid it is.
George Mallory, Chapters IV-VI, X-XI in
Bruce, CG, The Assault on Mount Everest 1922, page 129
