You can draw two rectangles and place them next to each other. And then rotate by 45 degrees. Modify the width/height/top/left parameters for any variation.
HTML
<span class="checkmark">
<div class="checkmark_stem"></div>
<div class="checkmark_kick"></div>
</span>
CSS
.checkmark {
display:inline-block;
width: 22px;
height:22px;
-ms-transform: rotate(45deg); /* IE 9 */
-webkit-transform: rotate(45deg); /* Chrome, Safari, Opera */
transform: rotate(45deg);
}
.checkmark_stem {
position: absolute;
width:3px;
height:9px;
background-color:#ccc;
left:11px;
top:6px;
}
.checkmark_kick {
position: absolute;
width:3px;
height:3px;
background-color:#ccc;
left:8px;
top:12px;
}