S and W coins are rarely, if ever, found in general circulation, although S coins bearing dates prior to the mid-1970s are in circulation. Denver coins bear a letter D, San Francisco coins bear a letter S, and West Point coins bear a letter W. Among marked coins, Philadelphia coins bear a letter P. Unmarked coins are issued by the Philadelphia mint. The identifying letter of the mint can be found on the front side of most coins, and is often placed near the year. The producing mint of each coin may be easily identified, as most coins bear a mint mark. The proof and mint sets are manufactured each year and contain examples of all of the year's circulating coins. Philadelphia and Denver produce the dies used at all of the mints.
The West Point Mint produces bullion coinage (including proofs). The San Francisco Mint produces regular and silver proof coinage, and produced circulating coinage until the 1970s. The Denver Mint also produces circulating coinage, mint sets and commemoratives. The main mint is the Philadelphia Mint, which produces circulating coinage, mint sets and some commemorative coins. Today, four mints operate in the United States producing billions of coins each year.
