Revelation 9:4

They were told not to harm the grass, or any plant, or any tree, but only those who have not 'the seal of God upon their foreheads.'

2 Corinthians 1:22

Also set his seal upon us, and gave us his Spirit in our hearts as a pledge of future blessings.

Revelation 14:1

Then, in my vision, I saw the Lamb standing on Mount Zion. With him were a hundred and forty-four thousand men, with his name and the name of his Father written on their foreheads.

Revelation 7:2-3

And, in the east, I saw another angel, ascending, holding the seal of the Living God; and he cried in a loud voice to the four angels, to whom there had been given power to harm the earth and the sea--

2 Timothy 2:19

Yet God's firm foundation still stands unmoved, and it bears this inscription-- 'THE LORD KNOWS THOSE WHO ARE HIS'; and this-- 'LET ALL THOSE WHO USE THE NAME OF THE LORD TURN AWAY FROM WICKEDNESS.'

Revelation 20:4

Then I saw thrones, and to those who took their seats upon them authority was given to act as judges. And I saw the souls of those who had been beheaded because of the testimony to Jesus and because of the Message of God, for they had refused to worship the Beast or its image, and had not received the brand on their foreheads and on their hands. They were restored to life, and they reigned with the Christ for a thousand years.

2 Corinthians 12:21

I am afraid lest, on my next visit, my God may humble me in regard to you, and that I may have to mourn over many who have long been sinning, and have not repented of the impurity, immorality, and sensuality, in which they have indulged.

Ephesians 4:30

And do not grieve God's Holy Spirit; for it was through that Spirit that God sealed you as his, against the Day of Redemption.

2 Peter 2:8-9

for, seeing and hearing what he did, as he lived his righteous life among them, day after day, Lot's righteous soul was tortured by their wicked doings.

Revelation 13:6-7

It opened its mouth only to blaspheme God, to blaspheme his Name and his Tabernacle-- those who dwell in his Tabernacle in Heaven.

Treasury of Scripture Knowledge

Summary

And the LORD said unto him, Go through the midst of the city, through the midst of Jerusalem, and set a mark upon the foreheads of the men that sigh and that cry for all the abominations that be done in the midst thereof.

General references

Bible References

That sigh

2 Corinthians 12:21
I am afraid lest, on my next visit, my God may humble me in regard to you, and that I may have to mourn over many who have long been sinning, and have not repented of the impurity, immorality, and sensuality, in which they have indulged.
2 Peter 2:8
for, seeing and hearing what he did, as he lived his righteous life among them, day after day, Lot's righteous soul was tortured by their wicked doings.

General references

Matthew 5:4
Blessed are the mourners, for they shall be comforted.
Romans 9:2
Bears me out when I say that there is a great weight of sorrow upon me and that my heart is never free from pain.