Question: What do you call the V-shaped figure one uses to check a checkbox? How about the X-shaped figure?

Answer: 
You might be looking for "check" or "tick", or "check mark" or "tick mark".
Do you mean a check mark (also called a tick)? <http://en.wikipedia.org/wiki/Check_mark>
The x-shaped mark can be called simply an x or a cross.<http://en.wikipedia.org/wiki/X_mark>