Were wolf birthmarks?

im writing a book and i need to know Your best idea of what a werwolf's birth mark might look like. there many saying and folklore behind this and what it should look like. Ive seen many sights but their are so many answers and so much information i can't look at it all, some don't even have to do with my question. so what should a were wolves birth mark look like. thank you so much to who ever answers.