red-flag

the symbol or banner of a left-wing revolutionary party.

a danger signal.

something that provokes an angry or hostile reaction: The talk about raising taxes was a red flag to many voters.

Also called powder flag. Nautical. a red burgee, designating in the International Code of Signals the letter “B,” flown by itself to show that a vessel is carrying, loading, or discharging explosives or highly inflammable material.

(initial capital letters) a war game the U.S. Air force holds several times each year at Nellis Air Force Base, Nevada, to train personnel in air combat.

to mark or draw attention to for a particular purpose: The department has red-flagged the most urgent repair work to be done.

to provoke the attention of; alert; arouse: The animal's refusal to eat red-flagged the keeper that something was wrong.

of or pertaining to a red flag.

intended or serving to emphasize, warn, incite, or provoke.