Private Sub xlApp_WorkbookOpen(ByVal Wb As Workbook)
    If Right(UCase(Wb.Name), 4) = "XLSM" Then
        If Wb.VBASigned = False Then
                MsgBox "The workbook '" & Wb.Name & "' is not signed. " & _
           "If there are auto-run macros in the workbook, " & _
           "they will not be run.", vbExclamation, "Signed Workbook Check"
        End If
    End If
End Sub