Abstract: An endcap header assembly includes a primary frame and an auxiliary frame. The primary frame includes a back wall, a top wall extending forwardly from the back wall, and a bottom wall extending forwardly from the back wall opposite the top wall to define a sign holder track in front of the back wall and at least partially open opposite the back wall. The auxiliary frame includes a primary panel, a top panel, and a bottom panel extending across a bottom of the primary panel. The top and bottom panels collectively define a first auxiliary sign reception track on a first side of the primary panel and a second auxiliary sign reception track on a second side of the primary panel. The auxiliary frame is configured to be slidably and selectively received within the sign holder reception track in a first configuration and a second configuration.