The Manual on Uniform Traffic Control Devices is a nationwide guideline perscribing how traffic control devices get built.  California adopts the MUTCD after it gets updated, and incorporates State-specific details in the process.  To see the latest MUTCD and how CA is planning to adopt it, see http://www.dot.ca.gov/hq/traffops/signtech/mutcdsupp/ca_mutcd2011_draftrevisions.htm