I think this is better, alot faster.
Private lngMs As Long 'Put this in the declarations area
Function IsMsBlockref(lngOwner As Long) As Boolean
If lngMs = 0 Then
lngMs = ThisDrawing.ModelSpace.ObjectID
End If
If lngOwner = lngMs Then IsMsBlockref = True
End Function
Sub TestisModelSpace()
Dim SS As AcadSelectionSet
Dim i As Integer
Set SS = sset(0, "insert")
For i = 0 To SS.Count - 1
Debug.Print IsMsBlockref(SS(i).OwnerID), i, SS(i).Name
Next
End Sub
Edited as Bob's use of modelspace was better than a string search