A tamper-resistant sign comprising a holder (l0) having a front wall (ll) spaced from a rear wall (l2) to define a sign chamber (l7) between the walls, and a sign panel (30) inserted in the sign chamber (l7). The sign panel (30) includes a retaining element (32) extending therefrom and a wall (l2) of the holder includes a recess (l8). The retaining element (32) and the recess (l8) are positioned in their respective elements so as to be aligned with one another when the sign panel (30) is fully inserted in the sign chamber (l7); the retaining element (32) is then received in the recess (l8) to restrict unauthorized removal of the sign panel (30) from the holder (l0).