nosebacon:

Police impersonation (impersonating a police officer) is the illegal act of portraying oneself as a member of law enforcement for the purpose of deception. Such acts are generally committed in order to assert police-like authority in order to commit some other crime. Posing as a police officer enables the offender to legitimize the appearance of his/her illegal act, such as gaining entry into a victim’s house, making a traffic stop, or detaining. According to the FBI, approximately 10,000 crimes are committed each year in which the offender impersonates a police officer.

Dressing up as a police officer in costume, or pretending to be a police officer for the purpose of play or a harmless prank toward an acquaintance is generally not considered a crime, provided that those involved recognize the imposter is not a real police officer, and the imposter is not trying to deceive those involved into thinking s/he is.

Police impersonation has often been committed in the following manners:

• Verbal indentification: The imposter announces to the unsuspecting victim that s/he is a police officer, leading the victim to believe it.
• Fake badge: The imposter, though not in any special clothes, displays a police-like badge to the victim. While a real police officer will be able to differentiate between the real and fake badge, the average individual may not.
• Fake uniform: The imposter wears a uniform that looks very much like that of a police officer, leading the victim to not think twice.
• Fake vehicle: The imposter places lights, decals, or other equipment on a personal vehicle to disguise it as a police car and enable the offender to make arrests or traffic stops.

Read more: What constitutes impersonation of a police officer Example - JustAnswer http://www.justanswer.com/law/1ifqv-constitutes-impersonation-police-officer-example.html#ixzz1x9dCzxpH