I think it has more to do with certain lines than with all hets having the marker. ALL of my hets have strong markers, and the possible hets with markers I've sold to friends have proven out.
Even my pastel het pieds have very strong markers.
het pied
As I've been saying for a few years, it's more than just stripes along the belly. Look at the yellow smudging on the belly as well. Another marker IMHO.