I know that when I have done it in certain places on my body then it's a sign of things are getting too severe in terms of my SI. It may be not as deep as some of my "preferred" places to cut but it's still worrying. I may not be the best person to ask as I havent cut in a long time.
Fyi OP we use the term SI to mean self injury here. It's rare that someone uses the term suicidal idealation we tend to use the term suicide. Or OD to mean overdose.