Why is S language called so ?

John Chambers :
_Rick Becker’s document describes the naming process, and dates it to July. We cast around for various names, getting suggestions from our colleagues, but without coming up with any satisfactory name that was not already taken. In the end, and with the C langauge as a precedent, we noted that the letter S was common to all the proposed acronyms, and chose the intersection. For the first couple of years, the letter was contained in single quotes, `S', but later undressed to a single character. (As we later found out, this had the side effect that we could not copyright it; single letters could not be copyright.)
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Link to the evolution of S : Version 1 of S