It stands for Schweizermesser shop - the vendor in Germany that sells them (and which doesn't ship internationally, as far as I can tell.)Victorinox recently changed its rules so all special alox SAKs have to be marked in some way. So Swissbianco has "Swissbianco" all over the blade (kind of ugly) and Schweizermesser has this fairly unobtrusive "S" logo. They have some fantastic regular Pioneers in all sorts of colours. The Pioneer X only came in red, green, black and blue and last time I checked red and blue were sold out.https://www.schweizermesser-shop.de/