One of the many quirks of Reporting Services we\'ve run across is the complete and utter lack of a CheckBox control or even something remotely similar.
What I have used to display a check box (or ballot box):
1- create textbox (that will become your check box)
2- change font to Arial Unicode MS
3- in the expression window use:
ChrW(&H2611) for a filled-in checkbox
ChrW(&H2610) for an empty checkbox