Abstract: The present invention relates to a vertical stacking system having a shelf support assembly for supporting the edge surface of the bottom surface of the bottom most signature in a stack of signatures. The shelf support assembly is positioned perpendicular and out of the path of a sliding support which receives the forming stack. The shelf support assembly is moved towards the forming stack and away from the formed stack at the same time forks of the sliding support are extended and retracted for receiving and releasing the stack of signatures.