How do you read and interpret IMO safety sign symbols correctly?

You read IMO safety sign symbols correctly by understanding the colour coding, pictogram category, and directional or supplementary text on each sign. Every element of an IMO symbol carries a standardised meaning defined under IMO Resolution A.752(18), so once you learn the system, any compliant sign on any vessel becomes immediately readable. The sections below break down each layer of that system, from colour meaning to positioning requirements.

What do the different colours on IMO safety signs mean?

Colour is the fastest communication tool on an IMO safety sign. Each background colour signals a specific type of message: green indicates safe conditions, escape routes, and emergency equipment locations. Red signals fire-fighting equipment or prohibition. Blue denotes mandatory actions. Yellow or amber warns of hazards. These colour conventions are consistent across all SOLAS-compliant vessels.

The logic behind this system is that crew and passengers can react correctly even before reading the pictogram in detail. A green sign tells you to move toward it in an emergency. A red sign draws attention to fire-fighting resources or warns you not to do something. A blue sign tells you that a specific action is required, such as wearing protective equipment. Yellow signs prompt caution and signal that a hazard is present nearby.

Understanding colour meaning is especially valuable in low-visibility conditions or during emergencies when cognitive load is high. Colour alone narrows interpretation to one of four possible message types, and the pictogram then delivers the specific instruction within that category.

What are the main categories of IMO safety sign symbols?

IMO safety sign symbols fall into five main categories: life-saving appliance signs, fire-fighting equipment signs, prohibition signs, mandatory action signs, and warning signs. Each category corresponds to a specific colour and pictogram style, and together they cover every safety communication need on a vessel, from routine operations to emergency evacuation.

Life-saving appliance signs use green backgrounds and direct crew and passengers to lifeboats, life jackets, muster stations, and escape routes. Fire-fighting signs use red to mark extinguishers, hose reels, fire alarm call points, and suppression system controls. Prohibition signs, also red, use a diagonal bar over a pictogram to indicate forbidden actions such as no smoking or no open flames.

Mandatory signs on a blue background instruct personnel to take a specific action, such as closing a watertight door or wearing breathing apparatus. Warning signs on yellow or amber backgrounds alert to hazards including electrical danger, flammable materials, or overhead obstacles. Knowing which category a sign belongs to allows you to interpret its intent before examining the specific pictogram in detail.

How do you decode a compound or combined IMO sign?

A compound IMO sign combines two or more symbols on a single panel to communicate a complete instruction in one visual unit. To decode it, read from left to right and treat each pictogram as a sequential element: the first symbol typically identifies the subject or location, and subsequent symbols add direction, action, or supplementary information. Arrows indicate the direction of travel.

For example, a green sign might show a running figure, a directional arrow, and a staircase symbol together, meaning “exit route via staircase in this direction.” Each element is standardised individually, so a compound sign is simply a combination of known components rather than an entirely new symbol to memorise.

When text supplements a compound sign, it reinforces rather than replaces the pictogram message. On multilingual vessels, the pictogram carries the primary meaning and text provides a language-specific confirmation. If you encounter a sign where the pictogram and text appear to conflict, the pictogram takes precedence under IMO conventions, and the sign should be reported for review.

What’s the difference between ISO 7010 and IMO A.752(18) symbols?

The key distinction is scope and application. ISO 7010 is a general international standard for safety signs used across industries including manufacturing, construction, and public spaces. IMO Resolution A.752(18) is specifically designed for maritime environments and incorporates symbols and requirements tailored to shipboard operations, evacuation procedures, and SOLAS compliance.

While many symbols overlap visually between the two standards, IMO A.752(18) includes maritime-specific pictograms that have no equivalent in ISO 7010, such as muster station signs, immersion suit locations, and embarkation ladder indicators. The IMO standard also specifies photoluminescent performance requirements appropriate for shipboard conditions, including exposure to moisture, salt air, and darkness below deck.

For vessels operating under SOLAS, IMO A.752(18) compliance is the mandatory benchmark. ISO 7010 signs may be appropriate for some onshore industrial areas on a vessel, but they cannot substitute for IMO-specific symbols in safety-critical locations. Procurement teams specifying maritime safety signs should always verify which standard applies to each location aboard the vessel.

Why do some IMO symbols look different across ships or manufacturers?

Variation in IMO symbol appearance across vessels typically comes from three sources: differences in the edition of the standard being applied, manufacturer interpretation of pictogram design within permitted tolerances, and legacy signs produced before current standards were adopted. While the core meaning must remain consistent, minor visual differences in line weight, figure proportions, or colour saturation are permitted within standard specifications.

IMO Resolution A.952(23) updated and expanded the symbol set originally established under A.752(18), so older vessels may still carry signs produced to the earlier resolution. Both remain recognisable in intent, but the updated symbols are more refined and easier to read at a distance or in poor lighting conditions.

Manufacturer quality also plays a significant role. Premium IMO safety signs, such as the New Generation IMO signs we produce at Signwell, are manufactured from PVC-free and halogen-free materials and meet photoluminescent performance levels that exceed minimum standard requirements by a factor of four. Lower-grade signs may be technically compliant on paper but perform poorly in the conditions they are designed for, which can create confusion when signs fade, discolour, or lose contrast over time.

How should IMO safety signs be positioned for correct interpretation?

IMO safety signs should be positioned at eye level, unobstructed, and at intervals that ensure continuous visual guidance along any escape route. The general principle is that a person at any point in a corridor or space should always be able to see at least one relevant sign without turning more than 180 degrees. Signs must remain visible in both normal lighting and emergency low-light conditions.

Height placement matters because it affects visibility when a space fills with smoke. Signs positioned too high become obscured early in a fire event. This is why Low Location Lighting systems complement overhead IMO signs by providing guidance at floor level, where visibility is maintained the longest during an emergency.

Directional arrows on escape route signs must be oriented accurately relative to the actual route. A sign installed on the wrong wall or with an arrow pointing in the wrong direction due to a mounting error is not just unhelpful but actively dangerous. During installation and post-installation inspection, each sign’s orientation should be verified against the vessel’s approved evacuation plan. Regular audits ensure that signs have not been obscured by new equipment, repainted over, or damaged in a way that compromises legibility.

For vessels requiring a full review of their maritime safety sign systems, including installation verification and compliance documentation, our DNV-certified inspectors carry out 3L-SI™ inspections that assess every sign against current IMO and SOLAS requirements.