I've been studying the letter/numbers John could see in the patch of blood next to the bible. I could be wrong but on checking the double photo of Shelia with the gun on her chest and then the other one where her arm is moved, the blood mark where the letter/numbers are... isn't there. Plus, the edge of the other photo where the U shaped blood would have been after her arm was moved has been cut off. Could this tell us that the blood mark John was speaking of was under the bible before Shelia's arm was moved?
Yes, the illegible number and word I could see in the carpet stain appeared at first to have been written in the blood, but on studying them again were more likely to have been impressions caused by someone (JB?) writing a letter on a sheet of paper which rested on top of the original CS photo. When this photo was subsequently photographed again, the impressions showed up... so another myth debunked before it even began.
The bible might have shifted slightly when her arm was moved, but not enough to make any difference to the position of the stain. It's difficult to tell, because in the dual photo (attached) the camera's location was changed for each shot. In the left pic the camera was held towards the foot of the bed, in the right pic it was held towards the head of the bed, so giving distorted views.
The mystery is... that the bible stain is abruptly cut off at the top of the page, which means that there should be a continuation of that stain on the carpet, somewhere between the arrows just above the top edge of the bible (in the second attached photo). The carpet stain (where I saw the mysterious number and word) is too far over to the right to have caused the bible stain, and even if it had would have been on the wrong (left-hand) page anyway.
As I said before, and as Caroline is definite about, I think the bible stain is a palm print caused by a woman's bloodied right hand, rather than from anything transferred off the carpet.