The default markers are
(*
{"\[FilledCircle]","\[FilledSquare]","\[FilledDiamond]","\[FilledUpTriangle]",
"\[FilledDownTriangle]","\[EmptyCircle]","\[EmptySquare]","\[EmptyDiamond]",
"\[EmptyUpTriangle]","\[EmptyDownTriangle]"}
*)
That list is from
Graphics`PlotMarkers[]