Crossword Clue:

a system of signals

AnswerCrossword Clue
MORSECODETelegraph-signals system
WINKSSignals of a sort.
CUESSignals of a sort.
NOVOTEIt signals a lack of support
MARKERSSignals at the rear of a train.
GONGFor example, leaving a holiday drink overturned can be what signals the start of dinner (4)