Where Is The Line Drawn For Counterstamp Legality?

Another time they got it right.

I can almost guarantee everyone they will kill their five cent coin before we do our cent.

The key word in the discussion is "fraudulent".

Putting a cent into one of those machines where it stretches the coin out into an oval shape as a souvenir of some place or another is certainly defacing the coin but not illegal.

On the other hand, gold-plating a Liberty Head Nickel that was issued without the word "Cents" on the reverse and then trying to pass it off as a $5 gold coin would be fraudulent and therefore illegal.

The real crime is that the United States Mint is still making cents when they have zero buying power and are thrown away, rot away, or are otherwise destroyed by the millions annually.

[/soapbox]

But to jump back on topic (sorry), I agree with most of the sentiments here. Legal or not, no one is going to care about counterstamps on a worthless piece of metal, unless, perhaps, you are "manufacturing" a rarity and trying to profit/defraud large scale.