Is The "Middle Finger" Allowed On A Front Book Cover, Or Is The Finger Too Obscene?

[Lana T.]

Have you seen a book with the middle finger on the front cover or is that just too obscene for a cover? I've never seen a book with the middle finger on the cover. I remember when the band Nirvana came out with their album Nevermind and Kurt Cobain gave the middle finger on the back of the album. But "that" was an album. What about books?

Thanks in advance!