It's not clear what you're asking. Are you referring to the letters that are part of the serial number on a bill? The printing-plate ID letters? Or the mint marks on coins? Please post a new and more specific question.
Assuming you are referring to seal letters, these are A through L and correspond to the 12 Federal Reserve Districts through which currency is distributed.
The basic currency used in the United States is the US dollar.
The official currency of the United States is the US dollar.The international currency code is USD.
The currency used in Las Vegas is the same as anywhere else in the US. The US dollar.
The current currency used by Denmark is the Danish krone.
Dollars USD
The US dollar.
USD... was there a currency change I was unaware about?
us dollars and cents
Us
The currency used by the United States is the United States Dollar, represented by the $ symbol.
The currency used by the United States is the United States Dollar, represented by the $ symbol.