If you're into graffiti, you should be aware of Jon Naar. His book 'The Birth Of Graffiti' / 'Faith of Graffiti' were one of a kind and showcased a graffiti culture and scene not yet documented at the time, mainly because it was still forming.
Naar, born 1920 was an English-American author and photographer celebrated for his pioneering images of New York City graffiti in the 1970s, and for portraits of Andy Warhol and other celebrities, including the British Prime Minister.
The book - a bible to most graffers - was shot over a few weeks of December 1972 in NYC. The numerous photographs were used in a similar book called 'The Faith of Graffiti' which was an essay written by Norman Mailer about the scene and the shots taken from Birth of Graffiti. Both books are considered an integral piece of graffiti documentation and history.
What you see in the book is the transition from signature graffiti to full-on block letter pieces. As the scene became more popular, taggers were looking to stand out amongst the growing crowd. Quantity was always helpful but size, color and quality were now the hot ticket. This is where we saw the emergence of block letters and the start of the block letter S being used.
Jon Naar's work provides a glimpse into a NYC scene and documents graffiti artists using the S in their designs. Whilst it doesn't solve any mystery to the origins of the S, it does hold a lot of significance to the timeline of how and why the S became so fun to draw.