Symbolism, Imagery, Allegory
In Chapter 9, God sends a mysterious angelic messenger to separate those who are going to be killed in the Babylonian invasion from those who aren't. The saved get a mark on their foreheads:
Now the glory of the God of Israel had gone up from the cherub on which it rested to the threshold of the house. The Lord called to the man clothed in linen, who had the writing case at his side; and said to him, 'o through the city, through Jerusalem, and put a mark on the foreheads of those who sigh and groan over all the abominations that are committed in it. To the others he said in my hearing, Pass through the city after him, and kill; your eye shall not spare, and you shall show no pity. Cut down old men, young men and young women, little children and women, but touch no one who has the mark. And begin at my sanctuary. So they began with the elders who were in front of the house. (9:3-6)
We just know you were about to say that this reminds you of the marking of doorways with sheep's blood on the first Passover, which saves the firstborn children of the Israelites from the Angel of Death who slaughters the Egyptians' firstborn (Exodus 12:23). It's also kinda like the marking God gives to Cain in Genesis which is meant to keep Cain safe during his exile, letting people know that he's a man protected by God (Genesis 4:15).
The image appears again in the Book of Revelation, where the righteous people who are saved by God also are marked on the forehead: "Then I looked, and there was the Lamb, standing on Mount Zion! And with him were one hundred forty-four thousand who had his name and his Father's name written on their foreheads." (Rev 14:1). Lots of imagery in Revelation is taken straight from Ezekiel. This was before copyrights.