Mint Marks
Mint Marks began being added to U.S. coins starting in 1838. Continuing to this day The Department of Engraving & Design's Die Manufacturing Division located within the Philadelphia Mint has produced nearly all Engravings/Galvanos, Master Hubs, Working Hubs, Master Dies and Working Dies used to produce all U.S coins (In 1996 the Denver Mint also began acting as an auxiliary die production facility when demand requires). Until the mid 1980's all working dies produced at the Philadelphia Mint had the Mint Mark hand punched into each one individually and sent to the various other Mint Branches for distribution with whatever the destination mint's MM letter was.
Sometimes impressing the MM into the working dies required multiple strikes and if there was movement or misalignment in between strikes a RPM could be created and passed on from the Working Die to all coins it was struck by. Beginning around 1965 the Mint Marks were hand punched into the Working Hubs instead of the Working Dies which cut down on the number of RPMs but they were still possible.
Beginning in 1985/86 for Proof Coins and the early 90s for normal Business Strikes the Mint Marks we no longer stamped into the working dies by hand rather engraved directly into the original design/plaster mold for all denominations. Due to this RPMs are not found on coins after about 1991.
Philadelphia, Pennsylvania (1793-Date, "P" Mint Mark or None)
Since inception this has been the main U.S. Mint facility coins struck in Philadelphia bear no Mint Mark with the exception of Wartime Nickels from 1942-54, Susan B. Anthony Dollars and all Philadelphia coins struck since 1979 besides the cent. The Philadelphia minted One Cent still does not have a MM.
Denver, Colorado (1906-Date, "D" Mint Mark) Created after major gold and silver discoveries in Colorado. Don't confuse the Denver "D" Mint Mark on coins from 1906 to date with the "D" mint mark on gold coins of 1838-61 struck at the Dahlonega, Georgia Mint.
West Point, New York (1984-Date, "W" Mint Mark)
West Point struck coins and commemorative medals beginning in 1974 although no mint marks appeared until 1983. From 1973 through 1986, the West Point Mint produced Lincoln Cents bearing no Mint Mark making them indistinguishable from those struck at the Philadelphia Mint. From 1977 to 1979 Bicentennial and Washington Quarters were also produced there. Beginning in 1983 a "W" mint mark was first used on the 1984 Olympic $10 gold eagles making it the legal tender U.S. gold coin since 1933.
In 1986 American Gold Eagle Bullions were produced in solely in West Point again with no mintmarks. Today all American Eagle series proof and uncirculated bullion coins in gold, silver and platinum are produced at West Point, along with all gold commemorative, some silver commemoratives and beginning in 2006 the American Buffalo Gold Bullion coins. All commemoratives from West Point are struck with the "W" mint mark. The West Point Bullion Depository was made an Official U.S. Mint Branch in 1988.
San Francisco, California (1854-Date, "S" Mint Mark)
Created after major California gold discoveries. No coins were minted in San Francisco from 1956-67. In 1968, it took over most proof coinage production from the Philadelphia Mint, but continued striking a circulating coinage from 1968 through 1974 as needed. Since 1975, the San Francisco Mint has been used only for proof coinage, with the exception of the Susan B. Anthony from 1979-81 and a portion of the cents minted in the early 1980s. The dollars bear a "S", but the cents are otherwise indistinguishable from those minted at Philadelphia which have no mintmarks, unlike those years' proof cents from San Francisco and circulation cents from Denver.
Denver, Colorado (1921-Date, "D" Mint Mark)
Established by an Act of Congress on April 21, 1862, the United States Mint at Denver opened for business in late 1863 as a United States Assay Office. Most of the gold came from the rich beds of placer gold found in the streams and first discovered in 1858, the same year Denver was founded.
Carson City, Nevada (1870-1893, "CC" Mint Mark)
Created after the discovery of The Comstock Lode. This Nevada mint was a short-lived facility and produced some of the scarcest coins in numismatics.
New Orleans, Louisiana (1838-1861 & 1879-1909, "O" Mint Mark)
After its closure in 1909, the building was used as an assay office until 1942, and was renovated as a museum in 1979.
New Orleans, Louisiana (1838-1861 & 1879-1909, "O" Mint Mark)
After its closure in 1909, the building was used as an assay office until 1942, and was renovated as a museum in 1979.
Charlotte, North Carolina (1838-1861, "C" Mint Mark)
Only gold coins were struck at the Charlotte Mint 1861 when it was taken by the Confederacy and never re-opened.
Dahlonega, Georgia (1838-1861, "D" Mint Mark)
Also only struck gold coins until it too was seized by the Confederate Forces in 1861 and never re-opened.