The crossword solution for the term SUPERMAN INSIGNIA is ESS, which stands for the iconic symbol of Superman's costume. The symbol is a stylized letter 'S' that is often referred to as the 'S-shield' or 'S-curl'. It has been featured in various forms of media, including comic books, television shows, and movies. The symbol is an instantly recognizable representation of the superhero and has become a popular symbol of heroism and justice.