...book cels are usually rather obvious...if 
there's a foreground element, especially if it's 
composed of some type of paper material (I've had 
book cels that had background-type paiting (no 
set outlines, gentle brush strokes, etc) painting 
done on an acetate foreground), it's book. They 
don't always, but they can say BOOK in big 
letters ^^

I've never had an experience w/ bank, so I don't 
know if there are any markings. But usually you 
can tell if it's from a bank sequence...

-Misha