This Peace Corps ad from 1966 is the first and possibly only instance I've ever seen of Superman's likeness being licensed solely to depict the character from the waist-down.
Since I'm talking about firsts, this is the earliest example I've yet found of newspapers using "Superman" to make reference to the comic book character, rather than a "super man." The photo sells it.
TARHELL TERROR FLIES THROUGH AIR LIKE SUPERMAN (Oct 29, 1939, The Philadelphia Inquirer)