Maybe it is possible that the cloud one carries around or the heaviness
or darkness or twisted-ness or depression that is very visible on a person is the mark.
Which could be considered a mark on the soul.Which enters His/Her thinking and work or actions,
which could be what is meant by the forehead or right hand, the location of the mark.
Possibly being sealed with God is that lightness, overjoyed, confident,Loved
look that people have when there soul is at peace with God.
You could say evidence of Light or lack of Light that shows outwardly could be a mark.
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