ETYM Latin enseigne, Latin insignia, pl. of insigne a distinctive mark, badge, flag; in + signum mark, sign. Related to Sign, Insignia, Ancient.
1. A flag flown by ship to show its nationality.
2. A person who holds a commissioned rank in the US Navy or Coast Guard; below lieutenant junior grade.

Piece of cloth used as an emblem or symbol for nationalistic, religious, or military displays, or as a means of signaling. Flags have been used since ancient times. Many localities and public bodies, as well as shipping lines, schools, and yacht clubs, have their own distinguishing flags.
symbolism
The Stars and Stripes, also called Old Glory, is the flag of the US; the 50 stars on a field of blue represent the 50 states now in the Union, and the 13 red and white stripes represent the 13 original colonies. Each state also has its own flag. The US presidential standard displays the American eagle, surrounded by 50 stars.
The British national flag, the Union Jack, unites the crosses of St George, St Andrew, and St Patrick, representing England, Scotland, and Ireland. The flags of Australia and New Zealand both incorporate the Union Jack, together with symbols of the Southern Cross constellation.
The flags of the Scandinavian countries bear crosses; the Danish Dannebrog (“strength of Denmark”) is the oldest national flag, used for 700 years. The Swiss flag inspired the Red Cross flag with colors reversed. Muslim states often incorporate in their flags the crescent emblem of Islam and the color green, also associated with their faith. Similarly Israel uses the Star of David and the color blue.
The flag of the former USSR placed the crossed hammer and sickle, which represented the workers of town and country, on a red field, the emblem of revolution.
The Canadian flag has a maple-leaf design and that of Japan a red disc symbolizing the sun.
signals
A flag is flown upside down to indicate distress; is dipped as a salute; and is flown at half-mast to show mourning. The “Blue Peter”, blue with a white center, announces that a vessel is about to sail; a flag half red and half white, that a pilot is on board. A yellow flag means “plague”.
1. An emblem flown as a symbol of nationality; SYN. national flag, ensign.
2. A rectangular piece of fabric used as a signalling device; SYN. signal flag.
3. Usually rectangular piece of cloth of distinctive design.
4. Stratified stone that splits into pieces suitable for paving; SYN. flagstone.
5. A conspicuously marked or shaped tail.
Any of various types of indicators used for identification of a condition or event; for example, a character that signals the termination of a transmission. + prikaži više

A flat stone used in paving, or any rock which will split into such stones.