My daughter is now 26 months old, she also has a "green vein" on her nose.
Old people said it means our babies will be difficult to bring up e.g. a bit weak or naughty. Well, believe it or not is upto us. To me, I don't believe it.
Anyway, you don't have to bring the baby to see doctor because of that.
my dad said it's bcoz of too much wind inside their body.....now, I try to "sweep wind" as often as I can..hope help la..my baby is only 2.5 months jar!