The term 'Sinister Sign' can be broken down into two crossword solutions: OMEN (4 letters) and Sinister (8 letters). An OMEN is an event or occurrence that is believed to portend a good or bad outcome in the future. It is often seen as a sign of warning or foreboding. Sinister is an adjective meaning threatening, dangerous, or evil. Together, these two words form the phrase 'Sinister Sign, ' which implies a warning of something bad or evil that is about to happen.