Revelation 9:4

They were told not to injure the grass of the earth or any plant or tree, but only the people who did not have the mark of God's seal on their foreheads.

2 Corinthians 1:22

and put His seal upon us, and given us His Spirit in our hearts as a first installment of future rewards.

Revelation 14:1

Then I looked, and there the Lamb was standing on Mount Zion, and with Him one hundred and forty-four thousand people who had His name and the name of His Father written on their foreheads.

Revelation 7:2-3

Then I saw another angel coming up from the east with the seal of the living God, and he cried out to the four angels who had the power to injure the earth and the sea:

2 Timothy 2:19

But God's foundation stands unshaken, with these inscriptions: "The Lord knows the people who belong to Him" and "Everyone who bears the name of the Lord must abstain from evil."

Revelation 20:4

Then I saw thrones and those who were seated on them, and permission was granted them to pass judgment, even those who had been beheaded for bearing testimony to Jesus and for preaching the word of God, who refused to worship the wild beast and his statue, and would not let his mark be stamped upon their foreheads and upon their hands. They lived and reigned with Christ a thousand years.

2 Corinthians 12:21

and that when I come back my God may humiliate me before you, and I may have to mourn over some of those who formerly have committed shocking sins, and have not repented for them -- their impurity, sexual immorality, and sensuality, which once they practiced.

Ephesians 4:30

You must stop offending the Holy Spirit of God by whom you have been stamped for the day of redemption.

2 Peter 2:8-9

for as long as that upright man was living among them, his upright soul, day and night, was always being tortured by what he saw and heard in their lawless actions --

Revelation 13:6-7

Then he opened his mouth to blaspheme against God, His name, and His dwelling place; that is, against those who live 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
and that when I come back my God may humiliate me before you, and I may have to mourn over some of those who formerly have committed shocking sins, and have not repented for them -- their impurity, sexual immorality, and sensuality, which once they practiced.
2 Peter 2:8
for as long as that upright man was living among them, his upright soul, day and night, was always being tortured by what he saw and heard in their lawless actions --

General references

Matthew 5:4
"Blessed are the mourners, for they will be comforted.
Romans 9:2
that I have deep grief and constant anguish in my heart;