Well the S-2 began in '48 and the New Departure factory flooded or something else destructive in '53 and sold out of stock by '54 or so. So it would date somewhere in there. The paint is in impeccable condition! Great find.
the link stated the ad as a 1950. Could of been on any number of bikes as I think it was kind of a "dealer" add on item. I could be wrong but that's my opinion.