What has been your experience with Mongolian Spots on baby?

My oldest had a Mongolian Spot--pretty large on her tailbone area. She's 10 now and it is completely gone. I ensured that her pediatrician put photographs of it in her medical file and always told sitters and daycare providers about it. Just a precaution for some overcautious "mandatory reporter" calling children's services to report a suspected case of abuse. Likely to never happen (and it never did), but I still wanted to take the precaution. Glad I did, though, because my grandma saw her in the bath and wanted to call the police on me for hurting that baby. My mom told her that my daughter had always had it.