Use the Wingdings font and put the following expression in the report object:
IIF(whatevervalueyouarechecking, CHR(252), CHR(251))
CHR(252) is a checkmark, CHR(251) is an "X". You can also play around with "o" and "x" which print an empty square and a square with an X respectively. Or CHR(253) and CHR(254) print squares with "X" and a checkmark respectively.
Cathy