Legal Question in Personal Injury in California

Yes.

Just to further clarify my answer, the "Star of Life" it technically a registered trademark of the U.S. Dept. of Transportation. It's use is regulated by the U.S. DOT and the GSA. As with many trademarks, there are infringing uses all over the place, hence the easy access anyone has to obtaining Star of Life stickers of various kinds. Technically, however, displaying it on any vehicle or equipment that is not authorized under DOT and GSA regulations and standards is an illegal use. There is no exception I have found for EMT's personal vehicles, but the CHP officer in the field has the authority to disregard infractions of state or federal regulations "in the interests of justice." So the officer is completely within his duties to ask you to show your EMT Cert. before deciding what to do about the unauthorized sticker.