Sorry for commenting so many times in a row here but I just had a flash back (not a ptsd "flashback") but to a fond memory from high school. I had a very artistic friend; we'd sit in the back of health class and every day she would draw a little green creature on my arm. It started as an alien with the green but it evolved into the great fun of "stick-figure-of-the-day." (Ohh yeah, the wonders of the American education system. How is it possible I read and write?? ha.)I've done that, and it helps up to a point. If the urge is stronger than that point, though, writing on my skin doesn't do it for me.
My mother actually expressed concern that the ink might be toxic! She had her moments... She thought I would come down with scurvy when I left for college. She does not remember this now, but I swear up and down she had this bizarre fear.
WAIT that's off the point.
The point is - when you are 16 years old, it is not very revolutionary to put ink on one's skin. I am glad I always went the non-permanent way - I have heard that people who self-harm tend to get more tattoos than average.
Also though if ink helps it is absolutely worthwhile to go with the pen. You are absolutely right - you've got to know the underlying reasons before coming up with any workable plan.