SquareSubsetEqual[x, y, ...] displays as x \[SquareSubsetEqual] y \[SquareSubsetEqual] ....
SquareSubset[x, y, ...] displays as x \[SquareSubset] y \[SquareSubset] ....
SquareSupersetEqual[x, y, ...] displays as x \[SquareSupersetEqual] y \[SquareSupersetEqual] ....
SquareSuperset[x, y, ...] displays as x \[SquareSuperset] y \[SquareSuperset] ....
SquareUnion[x, y, ...] displays as x \[SquareUnion] y \[SquareUnion] ....
Star
(Built-in Mathematica Symbol) Star[x, y, ...] displays as x\[Star]y\[Star]....
StartupSound is a global option that specifies whether Mathematica plays a sound when it is launched.
StringSkeleton[n] represents a sequence of n omitted characters in a string printed with Short. The standard print form for StringSkeleton is an ellipsis.
StructuredSelection is an option for Cell that specifies whether to allow only complete subexpressions in the cell to be selected interactively using the front end.
StyleNameDialogSettings -> {opt -> val} is a global option that specifies the cell style displayed in the Custom Style dialog box.