Folks, there's always lots of conjecture related to these passages, that's why I stated early on it's hard to be dogmatic about any of this... but just for consideration, there is another passage in Ezekiel where God had some men "marked" and others killed.

"And the glory of the God of Israel was gone up from the cherub, whereupon he was, to the threshold of the house. And he called to the man clothed with linen, which had the writer's inkhorn by his side;

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." Ezek. 9:3-4

So here the MARK was in the forehead which is kind of interesting when you compare that with Rev. 13:1, :16, :17...just food for thought.