An ensign is a distinguishing flag of a ship or a military unit; or a distinguishing token, emblem, or badge, such as a symbol of office. The word has also given rise to the military rank of "ensign", a rank of junior officer once responsible for bearing the ensign of his unit.

The word is derived from the French enseigne from the Latin plural insignia and is more particularly used for a military or naval standard or banner. An armorial ensign applies specifically to heraldic symbols of an army.

Maritime ensigns

In nautical use, an ensign in the form of a flag is usually flown at the stern of a ship or boat to indicate its nationality. Ensigns may also be flown from the gaff of a ship, and may be shifted to a yardarm when the ship is underway, where it is known as a steaming ensign. Vexillologists distinguish three varieties of a national flag when used as an ensign:

• A civil ensign (usage symbol

  

  

  

  Many countries don't distinguish between these uses, and employ their standard national flag in all three contexts; such a multiuse flag is termed a national ensign. Others (like the United Kingdom, Italy, Russia, South Africa, New Zealand, and Japan) use a variant of the national flag as the naval ensign. (Such flags are often strictly regulated as usable only on warships; civilian ships, with very few exceptions, would not fly naval ensigns.) Distinct civil ensigns are also common. In rare cases a distinct design is used for the state ensign, such as the blue ensign of the United Kingdom.

  If a warship goes into battle, large versions of naval ensigns (called battle ensigns) are used.

  Heraldric ensigns

  In heraldry, an ensign is the ornament or sign, such as the crown, coronet, or mitre, borne above the charge or arms.

  Military standards

  In many modern militaries, a "standard" refers to a type of ensign placed on a vehicle to indicate the rank of the occupant. This may be in the form of a decal on a windshield (such as the blue decals used to mark officers' cars in the United States armed forces), a license plate depicting an officer's rank insigne, or a small flag mounted on the hood or fender. These are the "standards" referred to in the 10th General Order for Sentries used by the United States Navy, which require subordinates to salute when the flags or placards are displayed "not cased."