Synonyms to warning sign

danger sign, early symptom, falling barometer, gathering clouds, high sign, omen, precursor, preliminary sign, premonitory sign, premonitory symptom, prodroma, prodrome, quarantine flag, red flag, red light, skull and crossbones, storm petrel, stormy petrel, symptom, thundercloud, thunderhead, warning signal, yellow flag, yellow jack, angry clouds, black cat, black clouds, blackening, blocking the light, breakers ahead, broken mirror, cardhouse, cause for alarm, clouding, crisis, danger, dangerous ground, darkening, dimming, eclipsing, emergency, endangerment, extinguishment, gaping chasm, halcyon bird, hazard, house of cards, imperilment, jeopardy, menace, obfuscation, obnubilation, obscuration, obscurement, obumbration, occulting, overcast, overclouding, overshading, overshadowing, overshadowment, owl, pass, peril, pinch, plight, predicament, quicksand, rainbow, raven, risk