The Book Switch Theory

[asteckley]

We cannot therefore say with any certainty exactly how visible it was based on these images. 

Here is another observation that may be relevant to the question of whether the signature should have been noticed, but it is just a minor one:

Lisa Fagin-Davis' paleographic analysis of the marginalia on the same page suggested that they are in the hand of Marci himself. The marginalia appear to be scratch notes written out as a mental aid while thinking about possible decipherment of the Voynichese—showing its alphabet and possible substitution with a Latin alphabet. The point is that they were not an attempt to record some cipher key that was even remotely close to “success”—they were made as working notes.

It is very difficult to believe that anyone—let alone someone who obviously valued the manuscript and considered it to be of great interest—would so cavalierly mar the pages of the manuscript itself with trivial scratch notes that were merely an aid to their thinking—not even a proposed final solution that they might have thought worth recording directly on the page.

But the minor observation is this:
Someone—supposedly Marci himself—spent a good deal of time up close and personal on that very page (and probably in good lighting) as he wrote letters and symbols in the same micro-sized writing as the main text. That fact just adds to the overall likelihood that he would notice the faint signature on the same page. (There also happens to be plenty more extra space at the bottom of the page for making such scratch notes than where they were made. But on the other hand, the right-hand margin would have been more attractive for the purpose of the long vertical table.)