Damage after it left the US Mint. How? Only the person that did it would know. Not a Mint Error of any kind.
There are many things to look for. But that goes for all denominations and all years. Educate yourself what true Mint Errors are first. And remember this.. just because somthing looks different, strange or weird does not automatically make it a Mint Error.
First, check your coin book and determine what a 64 nickel should look like. Next, check your coins for anything that is different than the standard and put them aside for review. Then, take photos of one of the coins and submit to CT for evaluation and be sure to identify the issues of which you wish clarification.