This question came up in chat room "what will the Mark of Athena cover look like".
After thinking about it for awhile the cover started to apper in my mind. My guess is Jason, Percy, Annabeth, Leo, Piper, Hazel, and Frank will be in a corner of the cover with there backs turned away from the reader looking over the side of the Argo II into Rome. While the rest of the cover will be the Mark burning through the city. It shoulbe the same color as the Battle of the Labyrinth cover.
But this is only my opinion, what are your visions?