none of mine has ever left permanent scars.. I think it depends on the severity of the injuries.

edited to add: I also started again recently (just before starting T). I say started 'again', but when I was a teen/child SI took different forms and was not so calculated. it was more of an instant response to distress.. like banging my head on the wall, grabbing handfuls of my flesh and digging my nails in or pinching to the point of bruising. it was usually in an effort to keep quiet. as I got older, I played with safety pins a lot. piercing flesh near the surface, carving, that sort of thing... I still stick with safety pins, but I will actually just sit down and scratch up my arms with them, sometimes going over and over the same spot until it starts to draw blood. but I try to keep it less noticeable since I swim and don't really want my husband to notice.
so.... yeah.