My boyfriend has a small black ring under skin on scrotum

It looks black, maybe purple..but its about the size of this O exactly on his scrotum. He has just found it today, he has no other health problems. His penis and scrotum looks fine and normal, no itching or scaling of the skin. He has no symptoms.  I am wondering if it is some kind of ringworm, but I would think he would have other symptoms. Also I would have no clue how he would have gotten ringworm. Anyways please try to give me an idea or what it could be. It's odd looking but it doesn't look serious. Also it's flat, its not raised or nothing..no lump under it or around it.  

[ducky406]

I have no idea what it could be but it probably be a good idea to have a dermatologist or at least a regular gp look at it.