We should throw in that in the modern John Byrne revision, the “S” was designed by Pa and Clark Kent. (Ma designed the rest of the costume.)
You’ll note that in Pre-Crisis history, the “S” differed by era. The Superman of Earth-1 had the more traditional “S” of which we’re familiar, although it was slightly smaller than the more prominent S we see today. The Earth-2 Superman (who was the Superman that debuted in 1939) originally had a plain “S” in a rounder shield, and only later took the five-sided shape, but kept the plain “S.”
The Superman of Earth-3 had a “U.” That’s another story.