There's no left click you can tie into. You could base it on selection (either
the mouse or the keyboard), but you could use rightclick for this:

If that's ok, rightclick on the worksheet tab that should have this behavior.
Select view code and paste this into that code window:

Option Explicit
Private Sub Worksheet_BeforeRightClick(ByVal Target As Range, Cancel As Boolean)
If Target.Cells.Count 1 Then Exit Sub
If Intersect(Target, Me.Range("a:a")) Is Nothing Then
Exit Sub
End If

With Target
If IsEmpty(.Value) Then
.Value = Chr(252)
.Font.Name = "Wingdings"
Else
.ClearContents
End If
End With
Cancel = True
End Sub

I used column A (range("a:a")), but you could specify any cells you wanted:

me.range("a1:b3,d9:f12,c:c")
for example.

FVC wrote:

Can I format (via Macro???) a cell so that if the user left clicks on the
cell a check mark appears without using the Control Toolbox. The cells with
such format will only need to then be the totaled (via =counta(x:x).

--

Dave Peterson