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U.S. Title 18, Chapter 17, Section 331: Prohibits among other things, fraudulent alteration and mutilation of coins. This statue does not, however, prohibit the mutilation of coins if done without fraudulent intent if the mutilated coins are not used fraudulently.
STATUTE-
Whoever fraudulently alters, defaces, mutilates, impairs, diminishes, falsifies, scales, or lightens any of the coins coined at the mints of the United States, or any foreign coins which are by law made current or are in actual use or circulation as money within the United States; or Whoever fraudulently possesses, passes, utters, publishes, or sells, or attempts to pass, utter, publish, or sell, or brings into the United States, any such coin, knowing the same to be altered, defaced, mutilated, impaired, diminished, falsified, scaled, or lightened - Shall be fined under this title or imprisoned not more than five years, or both