The CHP officer was grasping at straws. This code section (see below) doesn't even come close to being relevant. It just gives statutory authority to the DOT. What would folks be charged with? Impersonating the DOT? 21350 seems totally bogus. Doesn't mean they couldn't come up with a more relevant code violation next time, though. Need to play this one smart. Someone at the scene should have a copy of the Vehicle Code, so folks know what they're dealing with if threatened again.

From: www.dmv.ca.gov/pubs/vctop/d11/vc21350.htm

CA Vehicle Code
State Authority
21350. The Department of Transportation shall place and maintain, or cause to be placed and maintained, with respect to highways under its jurisdiction, appropriate signs, signals and other traffic control devices as required hereunder, and may place and maintain, or cause to be placed and maintained, such appropriate signs, signals or other traffic control devices as may be authorized hereunder, or as may be necessary properly to indicate and to carry out the provisions of this code, or to warn or guide traffic upon the highways. The Department of Transportation may, with the consent of the local authorities, also place and maintain, or cause to be placed and maintained, in or along city streets and county roads, appropriate signs, signals and other traffic control devices, or may perform, or cause to be performed, such other work on city streets and county roads, as may be necessary or desirable to control, or direct traffic, or to facilitate traffic flow, to or from or on state highways.
Amended Ch. 648, Stats. 1974. Effective January 1, 1975. Supersedes Ch. 545.