The pain drawings for each entry are meant to show where your pain is and how bad the pain is in each area. The drawing that shows up under your name on posts such as this one, are meant to show where you experience pain the most and how bad it is on average, but you could also make it a superhero if you really wanted to.
It marks my area of pain. It helps me see others are dealing with pain the same as mine, less than mine or worst than mine. Either way it lets me know I am not alone many times when I feel alone. Pain isn't something others can see. This gives a visual.