What characters can be used for up/down triangle (arrow without stem) for display in HTML?

Since you're using these arrows for a toggle switch you may want to consider creating these arrows with an html element using the following styles instead of unicode characters.

.upparrow {
   height: 0;
   width: 0;
   border: 4px solid transparent;
   border-bottom-color: #000;
}

.downarrow {
   height: 0;
   width: 0;
   border: 4px solid transparent;
   border-top-color: #000;
}

http://jsfiddle.net/FrsGR/