Significance of "cross" on cover page?
The uses of crosses is purely stylistic for different reasons, except for the right most one. There's no reason to imply that they (the first two at least) have any set or additional meaning beyond artistic flair. 

The first one from the left mostly likely pairs symbolism of crosses and vampires. The second one from the left is there to imply a negative. 

The title more or less translates to "it's not love, but it's intentional." The cross there likely represents an "X" implying that it's not something but intentionally there. 

The third one on the right has a purpose, it's intended to associate to things together like Beauty x Beast. For a more detailed explanation consult this answer.