single progressive series for all house numbers. In Genoa, Savona and Florence houses are marked with black (sometimes blue in Florence) numbers; businesses are usually (but not always) given red numbers, giving up to two distinct, numerically overlapping series per street. Those of businesses are denoted in all other writing (documents, online directories, etc.) by the addition of the letter "r" for rosso (e.g. "Via dei Servi 21r"). Turkey In most of Turkey, currently the European house numbering scheme is applied. The Istanbul Metropolitan Municipality introduced new house numbering and street signs in 2007 by two official designers. Central and Eastern Europe In Central and Eastern Europe, with some exceptions, houses are typically numbered in the European style. Many streets, however, use the "boustrophedon" system. Austria A double numbering system has been used, similar to the system in the Czech Republic and Slovakia, which also were formerly parts of the Austro-Hungarian Empire. Czech Republic and Slovakia In some Czech and Slovak cities and settlements, two numbering systems are used concurrently. The basic house number is the "old" or "conscription number" (, ). The conscription number is unique within the municipal part (a village, a quarter, mostly for one cadastral area) or within a whole small municipality. For makeshift and recreational buildings in the Czech Republic, "registration number" () from a separate number series is used instead of the descriptive number. Typically, this number begins with zero or with the letter "E", or has different colour, or contains words like ("makeshift structure") or ("weekend house"), etc. In some settlements where streets have names (mostly in cities), "new" or "orientational numbers" (, ) are also used concurrently. The orientational numbers are arranged sequentially within the street or square. If the building is on a corner or has two sides, it can have two or more orientation numbers, one for each of the adjacent streets or squares. Solitary houses distant from named streets often have no orientation number. In some places, the name of a small quarter is used instead of a street name. If there is a new building between two older numbered ones, the orientation number is distinguished with an additional lower case letter (for example, the sequence could be 5, 7, 9, 9a, 9b, 9c, 11, 13). In the 1930–1950s in Brno, lower case letters were used for separate entrances of modern block houses perpendicular to the street. Either number