Stick figures are completely acceptible! There are actually a couple of well known web comics that are done entirely with stick figures. As a matter of fact, I am a fan of using the stick figure because it forces the viewer into engaging their imagination more. There is also something about the "stick figure" which stands out in our mind as an important icon that we should pay attention to. Think of the icons on bathroom doors, or cross-walks: stick figures! And the eye gravitates immediately to them wherever they appear.