The 'S' is the Sylvania 'S' probabally for the Fire control system I think that was in use in the cars as indicated on the racing icons site
http://www.racingicons.com/gt/1076k.jpg
Here is a link to an old ad with the logo.
http://antiqueradio.org/art/rn47022.jpg
Solved
Thanks Gerard!
http://www.racingicons.com/gt/1076k.jpg
Here is a link to an old ad with the logo.
http://antiqueradio.org/art/rn47022.jpg
Solved

Thanks Gerard!