Here's another way...
If the checkmark is to be the only thing in that cell:
Format the cell font to "Marlett" and enter a lower case a.
If there's to be more than just the checkmark in the same cell, enter whatever you want in whatever font you want, using a lower case a where you want the checkmark. Then (in the formula bar) highlight the lower case a and change the font on just that character to Marlett.