"Domestic terrorism--Americans attacking Americans because of U.S.-based extremist ideologies--comes in many forms in our post 9/11 world. To help educate the public, we've previously outlined two separate domestic terror threats--ecoterrorists/ animal rights extremists and lone offenders. Today, we look at a third threat--the 'sovereign citizen' extremist movement. Sovereign citizens are anti-government extremists who believe that even though they physically reside in this country, they are separate or 'sovereign' from the United States. As a result, they believe they don't have to answer to any government authority, including courts, taxing entities, motor vehicle departments, or law enforcement. This causes all kinds of problems--and crimes. For example, many sovereign citizens don't pay their taxes. They hold illegal courts that issue warrants for judges and police officers. They clog up the court system with frivolous lawsuits and liens against public officials to harass them. And they use fake money orders, personal checks, and the like at government agencies, banks, and businesses."
Federal Bureau of Investigation: http://www.fbi.gov/news/stories/2010/april/sovereigncitizens_041310