It could be a white square on a white surface the way Russian artist Malevich could have painted it, but is the front page of a mail art catalogue.
This white front page is an illustration of some of the problems you encounter when dealing with a messy mail art archive. Various items in the archive have little or no specific information that can tell us where it is from. We have to figure it out from different bits of information like a rubber stamp inside, a recognizable handwriting, a recognizable theme, information about the piece in another piece as so forth. It is like a murder scene, and you are Jessica Fletcher.
Actually we know from the catalogue’s colophone that Jean Noël Laszlo (FR) made it. Very simple in this particular case, but you get the point.
See also an earlier blog post about digging through the archive in Raiders of the lost artefacts.