Marking pens, also called skin scribes, are surgical marking pens used by doctors to draw scalpel lines on patients. They are non-toxic and are designed to draw right on the skin. It is not good practice to just draw a tattoo design on the body, since mistakes and changes are going to occur. Better to rework the design beforehand on paper and to transfer it with another method. The only reason the skin scribe is mentioned here is that it is a useful tool for touchup work, alterations or additions to a design already on the body. For this purpose, it is always handy to have a few ready for when you need them.