The M-22 highway sign has become iconic. The black-and-white logo graces cars and T-shirts, and even a wine label. For visitors like Jodi Olson of Aurora, Ill., the M-22 logo is a happy reminder ...

Originally, California’s road signs were black with white lettering, but the state changed them after a federal rule was extended to the states. A federal study found that blue-and-gold and ...