This certainly is one type of mark, I agree. The inner mark which denotes where we are on our journey.
I wonder though...what would cause the archetypal Cain to be shunned or at least noted by all even where he was a stranger and his deeds were not known?
The inner mark of the unawakened -- and the accompanying lack of higher chakra energy -- would generally only be widely noticeble if all others everywhere were awakened. I'm not certain how likely this would have been.
So I'm still thinking it may have been a physical feature of some kind. What is fascinating is that there is no description whatsoever...only conjecture.
Peace & blessings
7L
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Bound by conventions, people tend to reach for what is easy.
Here we must be unafraid of what is difficult.
For all living beings in nature must unfold in their particular way
and become themselves despite all opposition.
-- Rainer Maria Rilke