Styx is a classic American rock band from Chicago that formed in 1972 and is best known for melding hard rock, power ballads and synthesizers to produce lasting classics like 'Come Sail Away' and 'Renegade' (ask your parents or Spotify it).
It was during the late 70s / early 80's that rock bands were looking to harden their image from soft rock to heavy metal. And this showed on the album covers produced at the time.
Styx, Sacred Reich, Iron Maiden, Judas Priest and Def Leppard - were all moving in this direction and used very similar graphic type logo.
Here are a few examples of those logos as well as early album covers.
As someone born in the 80's I can personally vouch for the influence these bands had on generations of kids and their school folders, pencil cases and desks. Similar to the Suzuki logo, Styx's S in essence really is 'the S'. No, not perfect like the 14 line masterpiece on the right, but for those hard rockers out there, when talking about that nostalgic S, this was it.
Whilst we can dismiss this as the origin of the S, these musicians certainly had one of the biggest influences on the cultures the S is found in, even to this day.
A funny side-note, as Roger Gastman points out in his book Beyond the Streets, Styx's 11th studio album was titled 'Kilroy was Here' - another phenomenon with global virility. Is it a clue?