Watch for Falling Rocks

I live in the L.A. area, and I drive Mulholland Drive quite a bit. And on that road, there’s a blind hairpin turn to the left right along a cliff where just before it stands a sign proclaiming: “Watch for Falling Rocks”. But where it’s placed makes it impossible for a driver to do so without driving over the cliff and crashing into someone’s roof 100 feet below. So I have to wonder if the sign is for safety or the opposite.