I don't think that is California though..
https://app.leg.wa.gov/rcw/default.aspx?cite=46.61.305
RCWs > Title 46 > Chapter 46.61 > Section 46.61.305
(1) No person shall turn a vehicle or move right or left upon a roadway unless and until such movement can be made with reasonable safety nor without giving an appropriate signal in the manner hereinafter provided.
(2) A signal of intention to turn or move right or left when required shall be given continuously during not less than the last one hundred feet traveled by the vehicle before turning.
Do we think that every state in the US doesn't have a similar law?