eight that are, or have been, a part of the US Mint:

“CC”
Carson City, Nevada
“C”
Charlotte, North Carolina
“D”
Dahlonega, Georgia
“D”
Denver, Colorado (this facility was started long after Dahlonega closed, there is no problem identifying if the coin came from Dahlonega or Denver)
“O”
New Orleans
“P”
Philadelphia (because it was a primary mint used no mintmark for many years)
“S”
San Francisco
“W”
West Point

Coin articles:
How Can I Avoid Silver Eagle Coin Fraud and Other Fake Silver Coins?
Avoiding coin fraud boils down to one basic point: knowledge. If you want to avoid buying fake silver coins and becoming a victim of …

Before they even went on sale, uncirculated and proof 2009 American Eagle Silver Coins are temporarily suspended, according to a new United States Mint statement at its online store.
The popular silver coins are minted specifically for collectors, bearing the “W” mintmark to denote their striking at the Mint’s West Point facility.
2009 dollar coins are on hold for the same reasons sales of American Eagle Silver coins were canceled in 2008 (”unprecedented demand”) and the Mint’s need to focus on bullion versions of the coin, without “W” mintmark; bullion versions are …