countries, use of the audible and visual warnings affords the officer a degree of exemption from road traffic laws (such as the right to exceed speed limits, or to treat red stop lights as a yield sign) and may also suggest a duty on other motorists to yield for the police car and allow it to pass. Warning systems on a police vehicle can be of two types: passive or active. Passive visual warnings Passive visual warnings are the livery markings on the vehicle. Police vehicle markings usually make use of bright colors or strong contrast with the base color of the vehicle. Some police cars have retroreflective markings that reflect light for better visibility at night, though others may only have painted on or non-reflective markings. Examples of markings and designs used in police liveries include black and white, Battenburg markings, Sillitoe tartan, and "jam sandwich" markings. Police vehicle markings include, at the very least, the word "police" (or a similar applicable phrase if the agency does not use that term, such as "sheriff", "gendarmerie", "state trooper", "public safety" etc.) and the agency's name or jurisdiction (such as "national police" or "Chicago Police"). Also common are the agency's seal, the jurisdiction's seal, and a unit number. Text is usually in the national language or local language, though other languages may be used where appropriate, such as in ethnic enclaves or areas with large numbers of tourists. Unmarked vehicles generally lack passive visual warnings, while ghost cars have markings that are visible only at certain angles, such as from the rear or sides, making them appear unmarked when viewed from the front. Another unofficial passive visual warning of police vehicles can simply be the vehicle's silhouette if its use as a police car is common, such as that of the Ford Crown Victoria in North America, or the presence of emergency vehicle equipment on the vehicle, such as a pushbar or a roof-mounted lightbar. Active visual warnings Active visual warnings are the emergency lights on the vehicle. These lights are used while responding to attract the attention of other road users and coerce them into yielding for the police car to pass. The colors used by police car lights depend on the jurisdiction, though they are commonly blue and red. Several types of flashing lights are used, such as rotating beacons, halogen lamps, or LED strobes. Some agencies use arrow