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''Red flag'' is a term denoting various attention and awareness indicators and signals, both explicit and implicit. It can be used in various contexts usually as a warning or when things seem too good to be true〔(【引用サイトリンク】title=Reporter raised red flag on Madoff in 2001 )〕 as well as unexpectedly good results.〔(Surge in CRCT results raises ‘big red flag’ )〕 The earliest citation for "red flag" in the ''Oxford English Dictionary'' is from 1602 and shows that at that time the flag was used by military forces to indicate that they were preparing for battle.〔1602 Thomas Dekker, ''Satiromastix'', ''Wks.'' 1873 I. 233 ″What, dost summon a parlie, my little Drumsticke? tis too late: thou seest my red flag is hung out.″ 1666 ''Lond. Gaz.'' No. 91/4 ″That the Red Flag was out, both Fleets in sight of each other, expecting every hour fit weather to Engage.″〕 The earliest citation of "red flag" in the sense of a warning is dated 1777 and refers to a flag warning of flood.〔1777 Philip Thicknesse, ''Year's Journey'' I. iii. 23 There is a red flag hoisted gradually higher and higher, as the water flows into the harbour (Calais ).〕 The term and the expression "to raise the red flag" come from various usages of real flags throughout history. The semaphore red flag (or red light) on railways means an immediate stop, while a red flag is frequently flown by armed forces to warn the public of live fire exercises in progress, and is sometimes flown by ships carrying munitions (in this context it is actually the flag for the letter B in the International maritime signal flag alphabet, a red swallow-tailed flag). In many countries a red flag is flown to signify that an outdoor shooting range is in use. The United States Air Force refers to its largest annual exercise as red flag operation. Red flags are used for various signals in team sailing races (see Racing Rules of Sailing). A red flag warning is a signal of high wildfire danger and a red flag on the beach warns of dangerous water conditions (double red flags indicate beach closure). Red flags of various designs indicate dangerous wind and wave conditions for mariners. In auto racing, a red flag indicates a stop to the race due to dangerous conditions. A signal of danger or a problem can be referred to as a red flag, a usage that originated in the 18th century. The term "red flag" is used, e.g., during screening of communications, and refers to specific words or phrases encountered that might indicate relevance to the case. For example, email spam filters make use of such "red flags". ==See also== *Racing flags - The red flag *Red Flags Rule 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Red flag (signal)」の詳細全文を読む スポンサード リンク
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