Run the macro as design time and it adds 4 markers and fills them in (1,2,3,4,1,2,3,4,1,2,3,4, ....)
[vba]
Option Explicit
Sub AddMarkers()
Dim oPres As Presentation
Dim oSlide As Slide
Dim oShape As Shape
Dim aBox(0 To 3) As Shape
Dim i As Long
Set oPres = ActivePresentation
For Each oSlide In oPres.Slides
On Error Resume Next
oSlide.Shapes("Box0").Delete
oSlide.Shapes("Box1").Delete
oSlide.Shapes("Box2").Delete
oSlide.Shapes("Box3").Delete
On Error GoTo 0
Next
For Each oSlide In oPres.Slides
For i = 0 To 3
Set aBox(i) = oSlide.Shapes.AddShape(msoShapeRectangle, 12 * i, 0, 12, 12)
aBox(i).Name = "Box" & i
aBox(i).Fill.ForeColor.RGB = RGB(0, 0, 0)
aBox(i).Line.Weight = 1
aBox(i).Line.ForeColor.RGB = RGB(255, 255, 255)
Next i
Next
For Each oSlide In oPres.Slides
i = (oSlide.SlideNumber Mod 4)
oSlide.Shapes("Box" & i).Fill.ForeColor.RGB = RGB(255, 0, 0)
Next
End Sub
[/vba]
Pretty crude, but it might help. The attachment has a sample result