A few years ago Lynn and I visited the Harry S Truman Library in Independence, Missouri. We learned a lot about the 33rd president including what I consider a bit of useless trivia.
Technically President Truman did not have a middle name. The letter "S" was used to honor his two grandfathers. Because the president didn't have a middle name a controversy has arisen about the use of a period after the middle initial. In 1962 Truman himself said that because he had no middle name the "S" should not be followed by a period.
Later it was decided by several style manuals, including the U.S. Government Printing Office Style Manual, that a period should be placed after the middle initial "S". As a result of Truman's statement in 1962, some authors will omit the period after the "S". With that said, Mister Truman did use a period after his middle initial in his signature.
So now you know a bit of trivia about the 33rd president's name for whatever it's worth.