Perhaps this sign on US 101 northbound just south of Santa Maria is a throwback to an earlier time. Instead of black letters on a white shield, a simple outline is used with no change in color.
Also notice the distinctive California usage of having the word "Business" come after the route designation. This is quite common in the state, but usually the route number isn't enclosed in a shield or state "miner's spade" outline.
This photo was taken in August 2003.