Tughra

A tughra () is a calligraphic monogram, seal or signature of a sultan that was affixed to all official documents and correspondence. It was also carved on his seal and stamped on the coins minted during his reign. Very elaborate decorated versions were created for important documents that were also works of art in the tradition of Ottoman illumination, such as the example of Suleiman the Magnificent in the gallery below.
The tughra was designed at the beginning of the sultan's reign and drawn by the court calligrapher or "nişancı" on written documents. The first tughra belonged to Orhan I (1284–1359), the second ruler of the Ottoman Empire and it evolved until it reached the classical form in the tughra of Sultan Suleiman the Magnificent (1494–1566).
Tughras served a purpose similar to the cartouche in ancient Egypt or the Royal Cypher of British monarchs. Every Ottoman sultan had his own individual tughra.
Visual elements of a tughra.
The tughra has a characteristic form, two loops on the left side, three vertical lines in the middle, stacked writing on the bottom and two extensions to the right. Each of these elements has a specific meaning, and together they make up the form that is easily recognizable as a tughra. 
The name of the sultan is written out in the bottom section, called a "sere". Depending on the period, this name can be as simple as Orhan, son of Osman in the first tughra in 1326. In later periods honorifics and prayers are also added to the name of the tughra holder and his father.
The loops to the left of the tughra are called "beyze", from Arabic meaning "egg". Some interpretations of tughra design claim that the beyzes are supposed to symbolize the two seas the sultans held sway over: the outer larger loop signifying the Mediterranean and the inner, smaller loop signifying the Black Sea.
The vertical lines on the top of the tughra are called "tuğ", or flagstaff. The three tugs signify independence. The S-shaped lines crossing the tugs are called "zülfe" and they, together with the tops of the tugs that also look to the right, signify that the winds blow from the east to the west, the traditional movement of the Ottomans.
The lines to the right of the tughra are called "hançer" and signify a sword, symbol of power and might.
Other tughras.
Although the tughra is largely identified with the Ottoman Sultans, they have also sometimes been used in other states, such as the Qajar dynasty, Safavid Empire and the Khanate of Kazan. Later, tughras were used among the Tatars of Imperial Russia.
The Mughal Emperors are also known to have used calligraphic symbols, alongside the Ottomans, the Mughal "Tughra" was circular in shape with three points at its tip, beside the calligraphic signature of the emperor.
Afghan currency notes from 1919 to 1936 had the tughra present as well. Pakistan had the tughra on it coins from 1947 till 1974; both of these are present in the State Bank Museum in Karachi. The nawab of Bahawalpur and the Nizam of Hyderabad had tugras on their coinage as well. The flowing lines could symbolize the wide reach of Suleyman's rule and his future conquests. It could also signify the spread of Islam to other realms beyond the Ottoman Empire.
Post-imperial interpretations.
There are modern artists of calligraphy that use the characteristic tughra form today. Examples are the tughras of Russian president Vladimir Putin and Akihito, the Emperor of Japan, created by artist Vladimir Popov.