Are you ready to rock hard--at least as hard as a copper and nickel alloy? Dustin and Stephanie can help. They cut and shape US coins into fully functional guitar picks. They're available as common coins, such as quarters and Sacagawea dollars, or antique coins, including buffalo nickels, wheat pennies and silver dollars.
"Whoever mutilates, cuts, disfigures, perforates, unites or cements together, or does any other thing to any bank bill, draft, note, or other evidence of debt issued by any national banking association, Federal Reserve Bank, or Federal Reserve System, with intent to render such item(s) unfit to be reissued, shall be fined under this title or imprisoned not more than six months, or both." - Title 18, Section 333 of the United States Code
Nothing in there about passing back into circulation. However these people might not have the necessary criminal intent.