Part 1; the history of the California Sign State Route Spade
Prior to the Sign State Route System, the US Route System and the Auto Trails were the only highways in California signed with reassurance markers. The creation of the US Route System by the American Association of State Highway Officials during November 1926 brought a system of standardized reassurance shields to major highways in California. Early efforts to create a Sign State Route System along lesser State Highways was initially spurred by the Auto Clubs.
Below prototype Sign State Route shields produced by the Auto Club of Southern California (ACSC) can be seen as they were displayed during 1929 (courtesy Robert Tyler of California's Porcelain Enamel Traffic Signs). The Sign State Route shield prototypes were of varying shapes and sizes, but all featured an iteration of the California Grizzley Bear. It seems the ACSC was interested in signing the Sign State Routes as they were numbered internally by the Division of Highways. These internal designations would be codified during 1933 into what were known as "Legislative Route Numbers." The ACSC also included designs for a County Sign Route shield.
The initial Sign State Routes were assigned to corridors of travel that were largely considered essential to state-wise transportation. While most Sign State Routes were applied over State owned Legislative Route Numbers not all were (example: California State Route 180 west over Panoche Pass to California State Routes 25 in Paicines).
The design of the Sign State Route shield was a borderless miner's spade which referenced the origin of the State of California during the Gold Rush in the years following the Mexican-American War. The Sign State Route shield was a white background with black numerals supplied by the ACSC and California State Automobile Association (CSAA). The initial Sign State Route featured the same California Grizzley which could also be found on the State Flag.