Abstract: A display apparatus is mountable on at least one of a dropped ceiling grid, a ceiling and a wall. The display apparatus is a partially enclosed structures having an open side. In one embodiment, there is at lease one hinge-fastener on a first side of the display apparatus adjacent to the open side is used for attaching said first side to a grid system member and at least one movable fastener on a second side of the display apparatus, opposite said first side, is used for releaseably attaching the second side to a grid system member. In another embodiment, the display apparatus is mounted by a rim extending around the open side of the display apparatus. A removable display unit is inserted into and removed from the display apparatus replacing information and advertisements therein.