The passive visual warnings are usually inherently linked to the design of the vehicle, and involve the use of high contrast patterns. Older vehicles (and those in developing countries) are more likely to have their pattern painted on, whereas modern vehicles generally carry the retro-reflective designs which reflect light from car headlights or torches (and was invented by 3M). 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.