Other books, like The Sign by Raymond Khoury, I can't really visualise as a movie. This is mostly because of the messy beginning, which takes time to figure out. And in a cinema, you need the viewers to understand almost immediately, because if not, they may lose the plot. And you end up with a lot of disappointed (and maybe angry) people.
The Sign is a thought-provoking book, which (once again), raises questions on the issue of knowledge (ToK student, ok Attempting to be a ToK student talking). The Sign is basically about how all religions are equal (religious pluralism) and how Christianity is ruining America.
As engaging as the plot is, the book was ruined towards the end for me, when the political and religious views were revealed. Looking at America from afar, where evolution is taught in schools as a fact and some students aren't allowed to pray, I highly doubt the claims about how Christianity in America is faring is true.
Another issue was how global warming was taken for fact. While one of the protagonists (there are a few), was initially a skeptic (i.e. before the book began), she was a whole-hearted believer by the beginning of the book. While I do think global warming is real, I'm not too happy about how that leads to evolution being taken as fact (and there's even a line that talks about the common sense of the scientist's who support evolution. I'm no science student, but it seems
Finally, the issue of religious pluralism. Religious pluralism basically says that all religions are equally true and valid, which is kinda contradictory. Can Father Jerome (a character in the novel) honestly say that everyone prays to the same God knowing that some religious have only one God (the Abrahamic religions) while others are pantheistic? Since Jesus has said that he is the only way to salvation, how is it that other religions also provide salvation? Not being an expert on other religions, I really can't comment on whether they believe there is only one way, or many ways.
The Sign, in conclusion, is a fairly good book in terms of plot. The characterisations, I think, is ok. But the view-points are very pointed, which may mar the enjoyment of the book for many people.