The paper produces the analyses of historical data about the applying the faked letters, falsification and identifying of individual handwritings and seals in Byzantium and Caliphate in the 10th century. In our paper we tried to analyze specific records of sources (Theophanes Continuatus, John Skylitzes, The Life of Euthymius, al-Masʻūdī etc.) about handwritings and its identifications. 10th century was the epoch of so-called «First Humanism», when a significant number of byzantine politicians and representatives of the byzantine upper classes gained access to the intellectual activities and became like professional literati. The same processes took place in Islamic world of Caliphate. Attainments connected with the identification of handw...