The term ELEMENT IN DINER SIGNS can be summarized as 'NEON', which is a four-letter element commonly used in diner signs. NEON is a chemical element with the symbol Ne and atomic number 10. It is a noble gas that is colorless, odorless, and tasteless. NEON is used in many applications, including lighting, advertising, and signage. It is especially popular in diner signs due to its bright, eye-catching colors.