Hmmm. An officer wearing a uniform is probably spotted as being one already? If the officer is not in uniform and not on duty, there exists no reason to identify himself or herself as a policeman. Let's have a law that all rapists, and all thieves, and all murderers (and other criminals and ex-cons) must identify themselves as being so during non-criminal encounters with the public. They might be practicing questionable and/or abusive behavior.