I'm no authority, but here's what I have on the S-40 toe.
From the SKIING September 1969: "Another major French manufacturer, Salomon, has come up with a lower- priced version of its Anti-Shock toe. It is called the S-40, and sells for $12. Although it operates on only one spring, it is said to have as much shock absorption as the double-spring Anti-Shock. Also, like the Anti-Shock, it requires no boot notching."
1970-1971 was a big year for Salomon bindings with the introduction of 3 new bindings - all matching toes and heels - S-505, S-502 and the S-404. The September 1970 issue of SKIING reported that the S-404 replaced the S-40 - looks like it was only around for 1 season.
I believe the the binding Phil mentions with the blue background and the silver S was the new S introduced in 1975-1976, reported by SKI to be "generally be sold in combination with skis and boots in package buys." I have an ad for that binding somewhere but have not been able to locate it at this point.
While I probably shouldn't post this here, does anyone have any insight on this little gem?
JB