To sign the log you will need to bring your own quill and ink.
Due to its location and the potential for it to be muggled, it is appreciated if you would not seek this hide out when it is dark, as the use of torches has the potential to give the hiding spot away. Many thanks.
Update 24 Feb 2016: Cache is back in place but has been moved approximately 11.5m WNW from its original hiding spot. The solution for the above puzzle has not been edited. Use Geocheck to obtain the new coordinates for the location.
To deduce the answer you will have to use your detective skills to find the volume number for each of these books.