Using WebDing or WingDing fonts is the only way to achieve the goal of this topic: it has to work starting with IE 6.0.2900. Therefore I would post some here, as well as some correction to posted above:
Cross_x000D_
<span style="font-family: Wingdings;">û</span><br>_x000D_
_x000D_
Check_x000D_
<span style="font-family: Wingdings;">ü</span><br>_x000D_
_x000D_
Crossed Checkbox_x000D_
<span style="font-family: Wingdings;">ý</span><br>_x000D_
_x000D_
Checked Checkbox_x000D_
<span style="font-family: Wingdings;">þ</span><br>_x000D_
_x000D_
Empty Checkbox_x000D_
<span style="font-family: Wingdings;">¨</span><br>_x000D_
_x000D_
Thick Check_x000D_
<span style="font-family: Webdings;">a</span>
_x000D_