Vessels sailing under the Gibraltar Country Flag are required to have on board this flag as part of flag state requirements that derive from maritime regulations in the International Code of Signals and the International Safety Management (ISM) Code. These codes are published by the International Maritime Organization (IMO) as an ongoing effort to reinforce maritime safety procedures and communications to the international maritime community. Fleet management companies and ship owners are responsible to ensure that each vessel in their respective fleets have the appropriate flag signage onboard to be in compliance. This flag is used to identify the flag state a vessel is sailing under and to communicate with other vessels under the provisions of the International Code of Signals.
The Gibraltar Country Flag is distinguished by a bicolor flag, white on the top half and red on the lower half. The white background is three times the width of the red. A red, two tiered castle graces the center of the flag, featuring three towers and appearing to be made from horizontally placed red bricks. The towers each contain a door with a rounded top at the top tier and a door with a rounded top at the bottom tier. The tiers are separated by a visibly protruding brick terrace where the lower portions of the top doors are depicted. A solid red base lies under the castle, which is separated from the lower red stripe as the castle is placed wholly in the white stripe. A golden key hangs from the base of the castle and intrudes into the red stripe. The key is rustic, having a diamond fixture designed in the main portion and two prongs which face toward the hoist, or left side. The Key symbolizes Gibraltar's geographic location, the Gateway to the Mediterranean Sea.