Just thought I would throw in my two cents. I never mark coins, and it also irritates me to find a nice AU clad coin with a sharpie mark on it. To mark them is illegal, although to my knowledge the only ones that got into trouble over circulated coins were the ones that took the state quarters and put the Silver Surfer sticker for the movie release on them.
http://www.msnbc.msn.com/id/18873168/
http://assembler.law.cornell.edu/us...tml/uscode18/usc_sec_18_00000331----000-.html
§ 331. Mutilation, diminution, and falsification of coins
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.
Happy Hunting
Scott (Mich)