This largely depends on what fonts you are willing to
use. One solution would be to select the Wingdings font
and use char(252). Most all installations of Excel come
with this font so it should be safe using this even if you
plan to distribute this workbook to other users.
If you prefer to stay with Arial, there is another pseudo-
solution. Beyond the normal 255 fonts is an Arial font
meant to be the Square Root symbol (√) which resembles a
check mark. This cannot be obtained with the char()
function. You can, however, bring up the Windows
Character Map utility, locate the character, copy it and
paste it in a cell.