Abstract: A modular system for forming a sign blank includes a plurality of midpanels preferably formed from resin reinforced with fiberglass. Each of the plurality of midpanels includes a face portion having a sign side and a back side and a key end opposite a channel end. A male key extends beyond the key end at the back side, and a female channel is located at the back side of the face portion, at the channel end such that two of the plurality of midpanels may be joined by interlocking the male key of one such midpanel with the female channel of another such midpanel.