What does the warning signal fr mean at the beginning?

traffic auxiliary police. According to Netease News, the alarm number is equivalent to the police's "ID card", and the alarm number fr is the traffic auxiliary police. It refers to the non-people police personnel who are recruited and used by local people's governments or public security organs at or above the county level to purchase services from social forces, sign labor contracts or employment contracts according to law, and provide auxiliary support for the daily operation and police activities of public security organs.