Here’s a clever project sent in by a designer in Italy:
"Get the pdf from the float box, and follow the instruction in it, or continue to read this post.
1) Print the pdf on an A4 paper, possibly on a borderless printer
(recycled paper is better for nature) or rescale it to a 95-98%…."
"6) Put the bookmark on the upper left or upper right angle of you book….enjoy it"
Fabio Sirna
Visit his blog.
Wow, very cool, thanks!
Chris
One can also cut the corner from an envelope to accomplish the same idea. I’ve been doing that for many years.
Please note that I do a new version, for Moleskine too. The permalink is the same, but I’ve updated picture (people do that I don’t know english lang
) and the pdf. 
Sorry sorry sorry for my mistake…next time in Italian
I don’t see the pdf file..