California Code, Vehicle Code - VEH § 21201.3

(a) A bicycle or motorized bicycle used by a peace officer, as defined in Section 830.1 of, subdivision (a), (b), (c), (d), (e), (f), (g), or (i) of Section 830.2 of, subdivision (b) or (d) of Section 830.31 of, subdivision (a) or (b) of Section 830.32 of, Section 830.33 of, subdivision (a) of Section 830.36 of, subdivision (a) of Section 830.4 of, or Section 830.6 of, the Penal Code, in the performance of the peace officer's duties, may display a steady or flashing blue warning light that is visible from the front, sides, or rear of the bicycle or motorized bicycle.

(b) No person shall display a steady or flashing blue warning light on a bicycle or motorized bicycle except as authorized under subdivision (a).