This icon is a part of a collection of MS SharePoint flat icons produced by Icons8. Icons follow the guidelines of iOS, Windows, and Android and are designed by a single designer, guaranteeing the consistent quality. Both PNG and vector are available.
It is a bold letter S in side a square slanted so that far left side appears to be further back than the near right side. There are two circles evenly spaced attached to the near right side and from then a simi circle is drawn to a 3rd circle of the same size as a point.