Abstract: An advertising box which can be attached to a post, such as a parking meter support post, comprises a pair of similarly-shaped, flexible flat panels, each panel including a four-sided center section hingedly connected along respective edges to an upper, lower and pair of side members that fold inwardly about the center section and contact along adjacent edges to form an open-sided, half-box assembly. The upper members, lower members and opposite side members of two-half box assemblies are fastened together with rust-resistant rivets to form a unitary structure about the post. The upper and lower members each include a U-shaped notch formed of a pair of spaced sides and a semicylindrical basin for accomodating a cylindrical post therebetween. The unitary structure is secured to the post with a banding clamp; two mounting brackets positioned about 180.degree. apart on the clamp; and a pair of bolts having security heads and sized to fit within threaded apertures in the mounting brackets.