ATD cover analysis
The final cover of Against the Day is pretty minimalist, depicting an aged, slightly yellowing book or manuscript in reference to the novel's setting, 1893 through World War I, and the book's mock-recreation of prose from that era.
The writing on the cover seems to cast shadows behind it. The shadows are no doubt meant to simulate the double refraction one experiences when looking through a piece of Iceland Spar, but on closer inspection the writing is not doubled, but tripled, and the typefaces are different. The upper layer is a modern sans-serif font, the middle layer is an older serif font, and the bottom layer is once again a modern sans-serif font. This may indicate that the novel straddles the period where the world moved from the 19th century into the modern age. It also may represent the book in parallel universes seen through the spar.
The mysterious red seal on the cover is Tibetan, and the image in the center of the seal is a Tibetan Snow Lion in front of three mountain peaks. The Snow Lion is a mythical creature which also appears in Tibet's flag.
The generally white color of the cover ties in with the light/dark metaphor that Pynchon weaves into the novel. Perhaps the cover is also largely bare so that the "reader can decide," as Pynchon writes in the book's description, with minimal outside interference from anything but the text itself.
The book cover is designed by Michael Ian Kaye, who also designed the cover for the current paperback edition of Slow Learner. This could indicate that Pynchon likes Kaye's previous work.
We also know that an earlier version of the cover was circulated in promotional material before the novel's release. Note that in the earlier cover, the mysterious red seal looks slightly different, with the writing continuing in an unbroken circle.
What exactly the seal means is no doubt revealed in the book, but the slight changes indicate that Pynchon was probably involved in the design process, as he was with Mason & Dixon (where the ampersand was changed at his request), and the cover is thus fair game in any textual analysis.