Mile Marker 420 Street Sign - 6" x 18" Authentic Reflective Aluminum Mile Marker 420 Street Sign - 6" x 18" Authentic Reflective Aluminum Mile Marker 420 Street Sign has the honeycomb aluminum causing it to be refective and authentic. Street Sign is made of reflective engineer grade prismatic reflective aluminum. High quality, will not fade. Thinkness of street sign aluminum is .080 gauge. Dimensions of street sign are 6" x 18". Corners are rounded and each end has a hole drilled for hanging/drilling purposes.