The main idea is that (spoilers for the book): each shaft symbolizes one of the characters, who died. The one with the cross - Rusty's grave, the spine - has half depth, referring to the general, who's half dead. Ink technique represents the oil, that made the family rich and which hides Rusty's body. On the left are the images of the hand-drawn font and a mockup of the book with a newly designed cover put over the original one.

 

A quote from the book, that inspired the idea:
"What did it matter where you lay once you were dead? In a dirty sump or in a marble tower on top of a high hill? You were dead, you were sleeping the big sleep, you were not bothered by things like that. Oil and water were the same as wind and air to you. You just slept the big sleep, not caring about the nastiness of how you died or where you fell. Me, I was part of the nastiness now. Far more a part of it than Rusty Regan was. But the old man didn't have to be. He could lie quiet in his canopied bed, with his bloodless hands folded on the sheet, waiting. His heart was a brief, uncertain murmur. His thoughts were as gray as ashes. And in a little while he too, like Rusty Regan, would be sleeping the big sleep."