What is the story behind the phrase "raise a flag"?
closed as general reference by FumbleFingers, Alenanno, Hugo, Mehper C. Palavuzlar, TimLymington Jan 16 '12 at 15:24
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There are so many situations where a physical flag is raised to draw attention to a problem or situation, that it's probably not possible to narrow down which one is responsible for the idiom.
- In sports, the linesman raises a flag when a foul is committed (to draw the referee's attention)
- A ship raises a particular kind of flag to signal distress etc.
- Before radio technology, flags would have been used extensively as signals in military operations
- Flags are still used in traffic control
Note also that "flag", as well as meaning as piece of cloth designed for display, also means anything used to draw attention.
raise a flag as an idiom seems to be present at least since the mid 19C in a sense similar to what it is used for in programming today.
ABA Jnl. Sep.1955 [v.41 p.819]
Publishers of legal services should annotate or cite applicable treaties which affect statutory law, or raise a flag in the preface that no consideration is given to treaty-made law.
This reference suggests that to 'raise a flag' means to 'call attention to ...' or 'announce prominently'.
Raise a flag means "bring something to notice". The phrase Raise a flag is originated from "raise a red flag" which means to alert someone about a potential danger or trouble ahead, the origin being that red flags are often literally used to warn people of possible peril.
Raise a flag has different meanings in different contexts.For example:- In Sports Raising a flag indicates an offside offence. And in the context of war Raise flag means Declaration of war. Also see Raising the first flag