Tughra

The tughra, the highly stylised calligraphic rendition of the sultan’s name, had long been affixed to official documents and put on coins. The parts of the tughra were composed by the calligrapher to a traditional design.

Courtesy of tugra.org

The tughra did have a written meaning, but was not really calligraphy to be read as words, but rather to be recognised as a symbol of the sultan.

The written meaning within the tughra of Sultan Abdulaziz III

Working within a tradition that forbade pictorial representation, on stamps the tughra served a similar purpose to representations of the monarch’s head on British stamps for example. To the Ottomans, the tughra represented the validating authority of the caliph and head of state and served this purpose up to the end of the empire.

The tughra of Sultan Abdulaziz III as it appeared on the first Ottoman stamps

Notably, the tughra did not appear on the Duloz and Empire stamps. 
© John Dunn.

The chosen motifs

Muslim tradition mitigated against a pictorial design and especially against a royal portrait. After a few seventh century imitations of Byzantine and Sassanid numismatic portraits, Muslim rulers nearly all abandoned portraiture on their coins until the twentieth century. Aversion to such portraits in official and religious art apparently stemmed not from any clear Quranic injunction but from a decision not to compete with highly-developed Byzantine and Sassanid iconography. Muslims poured their artistic energies instead into abstract geometric designs - the arabesque - and decorative calligraphy. Calligraphy became the main decoration on Muslim coins down through the centuries.

Crescent and star on 20 para Duloz issue 1865

Coat of arms on 20 paras of 1892

Tughra on 1863 20 paras issue

For exactly half a century (1863-1913) Ottoman stamps drew mainly on this Muslim tradition. Three specialised motifs - the tughra, a coat of arms and the crescent (sometimes accompanied by a star) - were employed on the stamps, along with the calligraphic, arabesque and baroque features described elsewhere. 
© John Dunn.