I'm referring to the gold spot/bar/stripe closest to the head (on the back of the neck). On most BPs this usually has a rounded end. On most visual Pieds and many Het Pieds it begins to split off to join with the gold face stripes.

I've been looking for this for months and I've seen this on a lot of Het Pieds, but not on very many normals or hets for other morphs. My theory is that this is a marker indicative of some, but not all, Het Pieds. Additionally, I don't think that this marker shows itself on non-Het Pieds like the train tracks do.