Since 2001, San Luis Obispo has replaced most of its street markers with these unusual markers using an uncial font, used in early medieval manuscripts. Perhaps there's some sort of intended association with the mission around which the town was founded. But to anyone knowledgeable about fonts, the effect is somewhat out of place.
I believe the font is a (slightly) photographically extended version of Libra, by the Dutch designer S. H. de Roos, released in 1939.
This photo was taken in September 2003.