I am a speech-language pathologist at a middle school. The majority of my students write on their hands and arms with pen and marker. I have one student whose parents get very upset with her when she does that and they tell her "people who write on themselves hate themselves." If there is any research that you are aware of or psychological information regarding this type of behavior please share! Thank you!
I taught Middle School for 12 years and saw this behavior frequently. Most students will do this as a habit which is not harmful, although there are extreme cases where students have put themselves at risk for health problems. Non harmful writing on the body may be due to boredom, communication to others, mimicking a tattoo (this is now a big fad), or simply wanting to identify with a symbol of significance such as the peace sign. Other students carry this to extreme using all colors of ink, and markers to express rebellion or get attention. There is evidence that overuse of these can be absorbed in to the bloodstream and introduce toxins in to the body. The risks are very similar to getting a Tattoo. Parents are justified when their kids carry this too far, and again behavior counseling may be necessary. There are no cases on record that a death has occurred but this behavior could be a gateway behavior to self mutilation with pens, or other sharp objects. At this point counseling is strongly encouraged and as a teacher, notifying the parents and students counselor should be paramount.