catchword clue cue cue word danger sign early symptom evidence falling barometer gathering clouds high sign hint hot lead intimation key key word lead omen precursor preliminary sign premonitory sign premonitory symptom prodroma prodrome quarantine flag red flag red light scent skull and crossbones spoor storm petrel stormy petrel suggestion symptom telltale thundercloud thunderhead tip-off trace vestige warning sign warning signal whiff yellow flag yellow jack