Nothing! He didn't have a middle name, per se. According to Truman himself, the initial was a way to honor both his grandfathers, Anderson Shipp Truman and Solomon Young.
Truman's middle name is just "S". This letter was chosen to honor both of his grandfathers, Anderson Shippe Truman and Solomon Young,
Harry S Truman
Harry Truman. The S. didn't stand for anything.
Harry S. Truman
"S" in Harry S. Truman doesn't actually stand for anything. His parents couldn't decide on a middle name, so they just went with the letter "S" as a placeholder. So, it's just Harry S. Truman, no fancy middle name to decode.
Harry S. Truman
Harry S. Truman was born on May 8, 1884.
He was born Harry S Truman
Harry Truman is not on money
Harry S Truman was US president at the end of World War 2 in 1945.Harry Truman
Harry S Truman. Please note that there is no period after the S in his name, because it isn't an initial letter abbreviation; the "S" doesn't stand for anything.
Harry S. Truman Harry S. Truman