I'm going to assume that means those who don't love God. I base this on the fact that generally speaking the mark of the beast refers to Satan's own, and the fact that these bowls were a judgment. They were meant to turn people's heart to repentance and a desire to give the glory to God.
In verse 2 we read:
2So the first angel went and poured out his bowl on the earth, and harmful and painful sores came upon the people who bore the mark of the beast and worshiped its image.A judgment on those who worship the beast, who bear his mark.
The second angel killed everything in the sea by turning it into like blood. As did the third angel turning the river waters into blood.
What caught my attention was this verse
5And I heard the angel in charge of the waters say,
"Just are you, O Holy One, who is and who was,
for you brought these judgments.
6For they have shed the blood of saints and prophets,
and you have given them blood to drink.
It is what they deserve!"
With this following response
7And I heard the altar saying,
"Yes, Lord God the Almighty,
true and just are your judgments!"
God is judging the peoples of the earth.
The angels knew it too! and they worshiped God through it.
8The fourth angel poured out his bowl on the sun, and it was allowed to scorch people with fire. 9They were scorched by the fierce heat, and they cursed the name of God who had power over these plagues. They did not repent and give him glory.
Not for the fifth angel.
10The fifth angel poured out his bowl on the throne of the beast, and its kingdom was plunged into darkness. People gnawed their tongues in anguish 11and cursed the God of heaven for their pain and sores. They did not repent of their deeds.Not for any of the angels and judgments did the peoples of the earth turn to God. The sixth angel's bowl dried up the Euphrates and then the beast sent forth evil spirits.
And the seventh bowl brought forth earthquakes and thunderstorms such as the earth has never experienced before. The peoples of the earth cursed God.
I have to admit, that as a believer I find it fascinating and unbelievable that even in the end times God wants people to turn to him. He judges them as a method of causing them to repent. And we don't! Those who have turned to Satan, those who have not turned to God, remain stubborn in their desire to not be OF GOD.Really shows who God is doesn't it.
I would have given up by now. But God remains forever the same, wanting this people to be HIS people. Bringing judgment for sure, but still with a call to repentance.
Blessed be the name of our Lord.