Emergency vehicles of any kind (fire truck, ambulance, police car) are highly likely to be involved in hazardous situations, including relatively common incidents such as a road traffic collision.
The passive visual warnings are usually inherently linked to the design of the vehicle, and involve the use of high contrast patterns.
Popular patterns include 'checker board' (alternate coloured squares, sometimes called 'Battenburg markings'), chevrons (arrowheads - often pointed towards the front of the vehicle if on the side, or pointing vertically upwards on the rear) or stripes (along the side - these were the first type or retro-reflective device introduced, as the original 3M reflective material only came in tape form).
In some countries, in addition to retro-reflective markings, the vehicles are now painted in a bright yellow or orange colour underneath, in order to maximise visual impact.
Another passive marking form is the name of the emergency service spelled out in reverse on the front of the vehicle (e.g. Ambulance or Fire).
Common colours for emergency vehicle warning beacons are blue and red, and this varies by country (and sometimes by operator).
Such devices include: Some emergency vehicle operators occasionally turn off their sirens when on side streets or when there are no cars on the road so as not to disturb residents; however, there is seldom a mandate for responders to do so.