Hello! That's a fantastic question, as 1921 was a very special year for U.S. silver dollars. Two different "Liberty" designs were minted that year: the Morgan Dollar and the Peace Dollar. The location of the mint mark depends on which of these two coins you have.
Let's break it down.
First, check if you have a Morgan Dollar. This design features a portrait of Lady Liberty with "E PLURIBUS UNUM" written above her head. If you flip this coin over to the reverse (the "tails" side), you'll see an eagle with its wings spread. The mint mark is located on this side, just below the eagle's tail feathers and centered above the letters "D" and "O" in the word "DOLLAR." For 1921, you might see a "D" for Denver or an "S" for San Francisco. If there is no mint mark, it was minted in Philadelphia.
Next, you might have the Peace Dollar. This was a new design introduced in late 1921. It shows a different, more modern-looking profile of Lady Liberty with a radiate crown. On the reverse side, you'll find an eagle at rest on a rock. The mint mark on a 1921 Peace Dollar is also on the reverse, but it's found below the word "ONE" in the phrase "ONE DOLLAR." Just like the Morgan, a "D" means it was from the Denver Mint and an "S" from the San Francisco Mint. No mint mark indicates it was made in Philadelphia.
The provided search information confirms that both Morgan and Peace dollars were made in 1921, which is key to answering your question. So, the first step is to identify which design you're holding, and then you'll know exactly where to look for that little letter
