i believe some people call it 'cell memory', my birthmark is on my right wrist and it's about the size of a 'flat circle tac'. [on top of my wrist and to the left] i'd love to learn more.
my mother and i have an identical [we already look very much alike] white circle/dot on our right hands between the bottom of the thumb and where your wrist meets your hand. our left ears are 'funny' at the tops and we also have the same sort of 'mark' on our cheek. [all circles] and all same spots. maybe it's just genetics but it's so interesting to me :)