Synonyms to preliminary sign

danger sign, early symptom, falling barometer, gathering clouds, high sign, omen, precursor, premonitory sign, premonitory symptom, prodroma, prodrome, quarantine flag, red flag, red light, skull and crossbones, storm petrel, stormy petrel, symptom, thundercloud, thunderhead, warning sign, 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