The concept of courtesy shield badges haven't been well clarified yet. According to some answers taken from a police forum about the topic the New Yor City Police Department (NYPD) give them to family members and close friends as a way to identify themselves as acquaintances to the NYPD and therefore as friendly, trustworthy people. Nevertheless in any other city or context out of NY such thing won't help you. On the contrary, it can be taken as if you were impersonating a police officer, which is a crime. Do not confuse them with the badge of the New York City Department of Sanitation (Police Enforcement Unit) that's a real one!