While the provided links suggest this is a popular question among collectors, the answer is a fascinating piece of American minting history. Discovering that 'P' on your nickel is your first step into a deeper story about where your money comes from.
That small 'P' is a mint mark, and it signifies that the coin was struck at the historic Philadelphia Mint. For most of its history, the Philadelphia Mint was considered the main U.S. Mint, and as a result, its coins didn't carry a mint mark. It was the default, the standard. If a coin had no mark, you simply knew it came from Philadelphia.
However, there are two key exceptions for the nickel that make this story interesting. The very first time a 'P' appeared on a Jefferson nickel was during World War II, from 1942 to 1945. To conserve nickel for the war effort, the composition of the coin was changed to an alloy containing silver. To clearly identify these special "war nickels," a large mint mark, including the 'P' for Philadelphia, was placed prominently above the dome of Monticello on the reverse.
After the war, the mint mark was removed from Philadelphia nickels again until 1980. Since that year, the 'P' has been a standard feature on all nickels produced there. So, when you see a 'P' on a nickel, you're looking at either a special silver coin from the World War II era or a standard nickel minted in 1980 or later. It's a simple letter that tells you a coin's origin and connects your pocket change to a specific moment in time.
