A proof coin is any coin that was created by the mint to be a proof coin. In the United States, proof coins are either minted at the San Francisco mint and contain an "S" mint mark, or at the West Point mint, containing a "W" mint mark. Depending on the year of mintage, though, proof coins have been struck in other mints, like Philadelphia. Generally, when the government creates proof coins, pennies, nickels, dimes, etc. are created in San Francisco and the more special bullion coins, containing the metals silver, gold, and platinum, are created at West Point. Examples of coins minted at the West Point mint is the 2017 American Eagle One Ounce Silver Coin.