Make Your Own Badge.

At OfficerStore.com, you can buy police equipments, such as batons, handcuffs, tire spike systems, and even real-lookin' badges.

The Internet is a wonderful place for cops wanna-be and criminals posing as fake cops.

Make your own shield: http://www.officerstore.com/store/shields-intro.cfm (via Spacegrinder and Boing Boing)

Update 5/5/06: OfficerStore wrote that to actually buy the badge that infer any police or security power, you need to provide identification.