The term 'Sign of Fire' can be broken down into two crossword solutions: SMOKE (5 letters) and CINDER (6 letters). SMOKE is a byproduct of combustion, which is the process of burning fuel. It is composed of tiny particles of carbon, ash, and other substances that are released into the air. CINDER is a type of solid residue that is left behind after a fire has been extinguished. It is usually made up of charred wood, ash, and other materials.