This sealing is identifiable by a mark on
the Israelites foreheads.

It is not certain if this mark can be seen by
human beings. Possibly by each other who
are sealed. For sure, it will be visible to the
angels who have the Trumpet Judgments.
It will be visible to the locust demons.

From Revelation 22:4 it looks as if all of
God's servants will have His Name on their
foreheads: "And they shall see his face; and
his name shall be in their foreheads."