Something which portends or is perceived to portend either a good or evil event or circumstance in the future, or which causes a foreboding; a portent or augury.
A thing of prophetic significance.
To divine or predict from omens.
To be an omen of.
A cue, warning, or alert; a sign or signal that something is wrong.
A signal that the race must be stopped immediately (and possibly restarted).
red rag
A common symbol, usually in the form of a banner, for leftist revolutionary ideologies, especially socialism.
In the United Kingdom and some other countries, a flag formerly used by a railway guard to warn the driver not to start the train.