Here is Bunny’s find of possible hidden numbers and letters in the tree on f71r of the Voynich Manuscript (link goes to original image). It is reproduced on my site with permission (by request, in fact).
Possible hidden letters and numbers in the tree in f71r.
Adjustments in the image: “changed contrast brightness, gamma, colour then made b/w. attempting to remove green from tree and clarify what left, no adjustments made to actual lines of image.”
Brian Cham's personal website 
One could also read them as numbers – say, 3, 2, 10 and below that [0]? I’m taking the Greek order: so GAMMA, BETA etc. The same would work for Hebrew, GIMMEL, BETH etc., and several others. Earliest known use of Arabic numerals in a Latin European text is ninth century, I think. A Mozarabic text.
Oddly enough the two characters are also those for ‘ten’ [+] and sun (no equivalent in this font). I’d dismiss it as co-incidence except that the stroke-order is perfect in both. The cross/+ sign would hardly matter, but that for the ‘sun’ is also perfect. left side, top-and-right-side, middle stroke, bottom stroke. Contrary to the usual method in western writing, which would draw the box and then insert the middle bar if it were a form, and if it were a ‘B’, then the right hand side and all the rest as one movement. Curious, isn’t it? Probably co-incidence of course, as are the hundreds of other instances of non-Latin European custom in this manuscript.