A sign system comprises one or more box-like modules having a front section and a corresponding rear section sized to fit together in sliding engagement to define an interior cavity. The sections may be joined together with fasteners which engage the side panels of each section thereby leaving the front and rear surfaces free of discontinuities. The sign modules may be affixed to a generally planar surface or supported on internal or external mounting posts. During installation, the rear section may be mounted first and the front section subsequently attached to the rear section. In this way only approximately one-half of the total weight of the sign need be lifted and manipulated at any one time thereby facilitating installation. The interior cavity defined by the front and rear sections may accommodate lighting means for internally lighting the sign.