Cal. MVC § 648

(a) Except as provided by subdivision (b), decorations authorized by this code and decorations, medals, badges, ribbons, and insignia authorized by the laws or regulations of the United States pertaining to the National Guard, Air National Guard, and Naval Militia may be worn by officers, warrant officers, and enlisted persons in accordance with the code, laws, or regulations. However, decorations awarded by other states and territories of the United States may be worn, but shall be subordinated to those issued by federal and state laws or regulations. No other decorations, medals, badges, ribbons, or insignia may be worn. A violation of this section shall constitute a misdemeanor.

(b) Decorations authorized by this code and decorations or medals from the Armed Forces of the United States, the California National Guard, State Guard, or Naval Militia, or any service medals or badges awarded to the members of such forces, may be worn by uniformed public safety personnel in accordance with the code, laws, or regulations, during the business week prior to Veterans Day and Memorial Day, the day of Veterans Day and Memorial Day, and the business day immediately following Veterans Day and Memorial Day. The employer of the uniformed public safety personnel shall retain the right to prohibit the wearing of military decorations pursuant to this subdivision if the employer determines that wearing the military decorations poses a safety hazard to the uniformed public safety personnel or to the public.