If you are not opposed to using some code, you can make this even friendlier than Outlaw's suggestion.
Download Example Workbook: Buckhorn36.297703.zip
Open a new workbook or download the example.
If, for instance, your check marks will be in range b2 to b30...
Range B2 to B30 is named "Checkmarks"
The font is set to WingDings2
Selecting a blank cell in this range will insert a checkmark
Selecting a cell that already contains a checkmark will remove it
Enlarge the font and center it for better viewing....
This code goes into the worksheet.
<table width="100%" border="1" bgcolor="White" style="filter
rogid:DXImageTransform.Microsoft.Gradient(endColorstr='#C0CFE2', startColorstr='#FFFFFF', gradientType='0');"><tr><TD><font size="2" face=Courier New> <font color="#0000A0">Private</font> <font color="#0000A0">Sub</font> Worksheet_SelectionChange(ByVal Target <font color="#0000A0">As</font> Range)
<font color="#0000A0">If</font> Target.Cells.Count = 1 <font color="#0000A0">Then</font>
<font color="#0000A0">If</font> <font color="#0000A0">Not</font> Intersect(Range("Checkmarks"), Target) <font color="#0000A0">Is</font> <font color="#0000A0">Nothing</font> <font color="#0000A0">Then</font>
Target = UCase(Target)
<font color="#0000A0">If</font> Target <> "P" <font color="#0000A0">Then</font> Target = "P" <font color="#0000A0">Else</font> Target = ""
<font color="#0000A0">End</font> <font color="#0000A0">If</font>
<font color="#0000A0">End</font> <font color="#0000A0">If</font>
<font color="#0000A0">End</font> <font color="#0000A0">Sub</font>
</FONT></td></tr></table><button onclick='document.all("10192007145257965").value=document.all("10192007145257965").value.replace(/<br \/>\s\s/g,"");document.all("10192007145257965").value=document.all("10192007145257965").value.replace(/<br \/>/g,"");window.clipboardData.setData("Text",document.all("10192007145257965").value);'>Copy to Clipboard</BUTTON><textarea style="position:absolute;visibility:hidden" name="10192007145257965" wrap="virtual">
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Cells.Count = 1 Then
If Not Intersect(Range("Checkmarks"), Target) Is Nothing Then
Target = UCase(Target)
If Target <> "P" Then Target = "P" Else Target = ""
End If
End If
End Sub</textarea>