I bought this coin myself from the US Mint in 2015. It also bears a W mint mark. As you see from the pictures, I have all the original packaging from the US Mint. The curved clip mint error is on the reverse above the word OF.
This error was written about by several coin news outlets. Here is one news article I found which explains the curved clip error. If you have any questions feel free to contact me. This item is in the category "Coins & Paper Money\Bullion\Silver\Coins". The seller is "rjm0222" and is located in this country: US.
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