You could use a font character for the checkmark,
some choices in   http://www.mvps.org/dmcritchie/rexx/htm/symbols.htm#ticks

Format Column A   as  "Wingdings 2"      and use a "P"  for the checkmark,
or choose a different checkmark from the above chart.    Then change
row 1  or cell A1 to normal font perhaps bolded.

Right click on the spreadsheet tab,   view code  and place the
following event code there you can take a choice of double-click event at
  http://www.mvps.org/dmcritchie/excel/event.htm#ticks.
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HTH,
David McRitchie, Microsoft MVP - Excel    [site changed  Nov. 2001]
My Excel Pages:  http://www.mvps.org/dmcritchie/excel/excel.htm
Search Page:        http://www.mvps.org/dmcritchie/excel/search.htm