I had this habit (let's say, i still have, but i've not been continuing this for more than a few months) where i doodled on my skin. Mostly on my left hand. Various objects were sketched, sometimes shabbily. Ranging from trees to abstract stuff (read weird shapes).
It saw a peak when i was in Mysuru. I used to choose various coloured markers (we carried them to mark our glassware in labs) to enhance the otherwise blue or black outlines (depending on a pen i could pick). But, i think i preferred black ink to blue ink.
Some of my friends considered this dirty and i was offered books in which i was to try out my drawing abilities. Some even came forward to allow me to colour their hands. One in particular warned that i'd contract some infection due to this prolonged abuse of my skin. That piece of advice was hardly given any attention.
Anyways, these days, i hardly use a pen on my dermis. But, i'd assume that some of those sketches were worth a look.