Abstract: An illuminated sign letter structure made up of an extruded plastic strip having a metal foil encased therein. One end of the strip is enlarged and has a ledge projecting outwardly from the strip. The opposite sides of the ledge are parallel and smooth for receiving the edges of a letter-form. The extruded plastic strip is formed into a letter shape and a letter-form of the letter shape is fixed in the frame to engage either the inner or the outer parallel, smooth ledge side. The metal foil may be straight or the end of the foil at the enlarged end of the extruded strip may be bent inwardly into the enlarged end.