It's perfectly fine to issue private currency in the United States, and that currency can be bartered, exchanged or used as payment in transactions. Entire communities have experimented with private currency, and several businesses in Detroit began accepting new Detroit Cheers bills instead of official money in 2009.

But when your private currency starts to resemble real money, federal prosecutors get very interested. And when your currency looks and feels like a real coin and says "Twenty Dollars" and "$20" on it, that's when the feds take action.

The maker of silver Liberty Dollars, Bernard von NotHaus, 67, was convicted last month for making and selling the private currency in the form of notes and coins, The Associated Press reports. And now the government wants to seize his stash of five tons of the silver dollars and precious metals, estimated at $7 million.

The question now is whether the maker of the Liberty Dollars tried to pass off the medallions as U.S. currency. The Constitution says that only Congress has the power to coin U.S. money and that only the U.S. Mint can mint and issue legal coins.

Van NotHaus' medallions had the words "Liberty," "Dollars" and "Trust in God" on them and showed such images as the Statue of Liberty's head and a flaming torch. They were advertised as "legal" and "constitutional," according to the U.S. Mint. People called the U.S. Mint asking whether the money was real, prompting the Mint to issue warnings that the dollars were privately produced.

Van NotHaus has claimed repeatedly that he never tried to pass the dollars off as real currency. He says he wanted to give local communities a transactional network based on an alternative, private currency. The medallions were reportedly made at a private mint in Idaho.

Private currencies are fine, but Liberty Dollars skirted too closely to the edge of legality. After his conviction, Van NotHaus faces up to 25 years in prison and a fine of $750,000, AP reported. He hasn't been sentenced yet.