The Mongolian mark is at the base of the spine, extending sometimes onto the buttocks, of newborns. It does not appear on legs. They usually fade, so you have to ask someone who knew and saw you and your cousins when you were infants. It is an unmistakable signifier of native American blood.
As I said my granddaughter had one but around here we attribute it to Mexican-American descent and it is mostly girls.
Ha! Wikipedia (and my quick scan of pages) again proves it is useless for accurate information. I will ask my mother then. Thanks for the correction.