Black Oxen is a reminder of the healthy benefits of cynicism, and in retrospect served as an early warning to an ebullient age.
While hindsight is always telescopic, there were early warning signs that the currency of Facebook shares was primed for a fall.
They have been an early warning signal by uncovering bad news.
Might this be an early warning sign of an art bubble about to burst?
They both deceived Aliandra, in spite of her father's early warning and her old aunt's anxious advice.
"Remember that an early warning of danger is valuable," Sir Thomas cried down to them from the poop.
Air defenses include surface-to-air missiles, antiaircraft artillery, and early warning and aircraft control sites.