a pencil. (commonly a number 2 pencil) It can either contain the lead (actually graphite) still inside or can just be particles that are visible through the skin. There is currently no way to remove it.
Number 2 Tatoo
The blue-gray mark left perminantly in your outer layer of skin (epidermis) after getting stabbed or stabbing yourself with with
Remember when you stabbed me with a pencil last year? I still have a number 2 tatoo.