A subtle signal is a nonverbal communication that conveys a message without the use of words. It can be used to indicate agreement, understanding, or to draw attention to something. The crossword solutions for the term 'subtle signal' are PSST (4 letters), WINK (4 letters), and NOD (3 letters). PSST is a sound made by whispering or hissing, usually to get someone's attention. A WINK is a facial expression made by closing one eye briefly. A NOD is a gesture made by lowering and raising the head slightly. All three of these signals are subtle ways to communicate without speaking.