California's state highway markers -- those green, numbered signs placed along local freeways and rural routes across the Golden State -- are so familiar a feature of the automotive landscape that it's easy to overlook their symbolism. But the shield accomplishes a neat trick. At once it points ahead and back -- forward toward some spatial destination, but also back toward a temporal point of origin. Its shape mimics the spade carried by Forty-Niners into the foothills and sold by the opportunistic merchants who made the real fortunes of the California Gold Rush.