6 Most Commonly Used ICS Flag Signals On Ships

by | Last updated May 9, 2024 | Navigation | 0 comments

Flag signals are one of the visual communication methods that many merchant vessels use today.

Whenever ships visit a port, you will always see these rectangular colored cloth hoisted on the forward or aft mast.

Also referred to as colors, seafarers use nautical flag signals for various reasons. Sometimes, they go with other lights and shape signals.

There are only 26 of them according to the International Code of Signals (ICS), but for this article, we will only discuss 5 of the most commonly used international maritime signal flags.

6 Flag Signals You Will Encounter On Board

You will likely use or encounter four ICS signal flags at sea, based on my experience during my decade of shipboard service.

I became more familiar with them during my cadetship when the captain assigned me the responsibility of hoisting and securing the appropriate colors when visiting a port.

1. Hotel (H) Flag

The Hotel flag is the ICS signal for the letter “H” and is probably the most widely used on board.

A ship hoisting this banner is announcing to everyone, saying, “I have a pilot on board.”

Easily identifiable, the Hotel flag has white and red color on the left and right half of the rectangular flag.

Since most merchant vessels visit ports, they eventually raise it on their mast to indicate that they have a pilot advising the captain’s actions.

The ship's aft mast flying its Hotel Flag indicating that he's navigating with a Pilot on board.
Hotel flag on the port side with the Turkish flag on the starboard.


White: This color occupies the left half of the flag.

Red: This color takes up the right half of the flag.

2. Bravo (B) Flag

The Bravo flag is a special flag normally hoisted on different classes of tanker ships, and it is easy to identify.

In the International Code of Signals (ICS), the Bravo flag (flag B) signifies that the vessel is:

  • Taking in dangerous goods/ cargoes
  • Discharging dangerous goods/ cargoes
  • Carrying hazardous goods/ cargoes

If you see ships flying the Bravo “red” flag on their mast, they are doing or carrying something hazardous.

Not only tankers but all other vessels as well. Those who are bunkering are considered “taking in dangerous goods” and must hoist the Bravo flag.

If in doubt, check the other vessel’s AIS to see their cargo and their condition.

A tanker ship in port performing cargo operation and displaying the red Bravo Flag on its mast.


The color of the Bravo pennant is full red.

3. Alfa (A) Flag

An Alfa flag is an ICS signal flag that means, “I have a diver down; keep well clear at slow speed.”

The ship displaying this blue and white banner has a diver inspecting or working on its underwater hull.

Aside from flying this color, the ship also announces via the VHF radio about its underwater works so everyone in the vicinity will slow down when passing.

Though not directly used as one of the tools for navigation such as Radar, ECDIS, or Navtex, you have to proceed with caution when seeing this flag.

I experienced hoisting the Alfa flag when we had our rudder inspected by a competent diver after we allegedly touched-bottom in Rostock, Germany.

A vessel hoisting an Alfa Flag.


White: This color occupies the left half of the flag.

Blue: This color takes up the right half of the flag.

4. Quebec (Q) Flag

The Quebec flag, also known as the “Quarantine” flag, is an internationally recognized signal flag that means “My vessel is healthy, and I require free pratique.”

A ship flying this yellow banner on its mast ensures the port authorities that it is free of any contagious diseases. Furthermore, it wants to enter the port and be cleared for entry by health officials.

After granted pratique, the ship can only then lower its Quebec banner, and allow port personnel onboard to do business.

You may see the quarantine flag displayed together with the Alfa, Bravo, and Hotel flags on a single ship and mostly on tankers!

Container ship with various flags including the yellow Quarantine or Quebec Flag.
Image: MarineTraffic Marjan Stropnik.


The Quebec (Q) flag is a yellow rectangular banner.

5. Oscar (O) Flag

An Oscar flag hoisted on the mast means a “Man Overboard” is currently happening. Because of that definition, seafarers call the Oscar flag as the Man Overboard Flag.

It’s not entirely a common flag, but I included this day signal because of its urgency. 

Nearby ships seeing this flag prompts them to keep a sharp lookout and assist in the rescue operation of the person falling on the water.

More importantly, they should check that ship if they are currently performing one of the Man Overboard maneuvers.

An Oscar Flag raised on the ship's mast.
Oscar Flag indicates man overboard.


The Oscar flag is a rectangular banner with two colors dividing it diagonally. The upper diagonal is red, and the lower diagonal is yellow.

6. November-Charlie (NC) Flag

While the previous five signal flags are single-letter banners, the November Charlie (NC) symbol is actually a double-letter pennant conveying life-and-death urgencies.

A November-Charlie (NC) flag on a vertical line is a form of distress signal that signifies the vessel is in need of immediate assistance.

November Charlie literally means “No-Yes,” which can be translated that he is confused, doesn’t know what to do, and requires urgent help!

A Novemver over Charlie Flag indicating a distress signal.

How to Use These Flag Signals

Seafarers widely use flag signals today. They are a redundancy feature since we don’t rely 100 percent on today’s modern tech.

If modern tools for navigation fail, like the Automatic Identification System or ARPA, flag signals can be very useful in identifying the status of vessels that display them.

To use these pennants, we simply tie both ends of the flag with a rope and hoist them on the appropriate mast—usually the bridge’s topmast during daylight hours, either during pilotage operation or port stay.

As I mentioned, you will probably use four or five of the 26 signal flags in the International Code of Signals.

May the winds be in your favor.



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