I remember when they started posting those signs and it was in the news briefly.
What had happened is that the gps maps said a road ran across a mountain range, but the gps maps did not specify the quality of the road, and people were driving on 4 wheel drive roads in their city cars.
Then they would get stuck about 15 miles from the paved (and trafficked road), and die of exposure. I think that there was one case of a family dying of exposure because they kept to their car about 500 feet from a road, hoping for rescue, and they were not found for a few weeks.
If you are reading this site, and traveling in the desert, I assume that you have a few jugs of water in your car, and some sort of shelter, which is much of what you need to self rescue. Though a land anchor, a long rope, a winch, and a tall jack would be helpful if you were driving on 4x4 roads in the desert.