The old warning signs on the left side of Groom Lake Road. In various flavors they tell you about the terrible things that will happen to you if you cross the border (which we strongly advise you NOT to do, EVER, for ANY reason). The white sign on top says it all: Use of deadly force authorized. Don't try if they mean it...
The sign saying that photography is prohibited, however, is only their way of telling you to take plenty of pictures. It has not been enforced since the early 1990's. Tourists from all over the world take photos at the signs all the time.