This document is a photograph taken of a brick wall with the S symbol painted on faintly in white paint. There is no writing on either side, either by Jen and Eric or anyone else, though there is a little writing about it on page 131.
The first thing to note is the back of the photograph has a faint logo saying “This paper manufactured by Spectra Photo.” Spectra Photo is a real company “That offers the full spectrum of business management and digital workflow solutions for photographers interested in building successful careers.” (Spectra Photo website)
Another interesting detail is that the lightning in the photograph itself seems to be coming up from below the wall, rather than straight-on, which would be the case if the light came from the camera, or from above, which would be the case if there was natural lighting. The fact that the lighting comes from below implies that there is an electric light illuminating the image, which would mean that the scene is one that has been recently set up, rather than old like Jen and Eric speculate.
Additionally, though the stones do look old, they do not look ancient; they are not very cracked, the cement is not crumbling, and the “S” symbol looks fairly fresh. This cold mean that this setup was constructed recently, possibly by someone else who is delving in to Straka and his works.
Photograph courtesy of http://sfiles22.blogspot.com/2013/01/list-of-inserts.html