The Banking Regulation and Supervision Agency has banned the use of simple combinations such as "1234", "4321", "1923", "1453", "1903", "1905", "1907" as PIN codes for bank cards.
If the first two examples are clear, then the rest may seem simple primarily to the Turks themselves. For example, in 1453, Constantinople was taken by the Ottoman Empire army, 1923 was the year Turkey was proclaimed a republic, and 1905 was the year Mustafa Kemal created the revolutionary organization "Vatan".
Bank customers who use such codes will be notified of the obligation to change them. Such precautions are introduced for security purposes and to prevent fraud.