The 14th century presents a new fashion in the Byzantine culture of writing with the intensified use of monograms and other abbreviations for different purposes and in different contexts. We could distinguish them in a luxurious group of Medieval Glazed ceramics with sgraffito decoration: plates, bowls and cups, produced mainly in Constantinople, which bear the monograms of different saints, placed underglaze, the emblem of the ruling Palaeologan dynasty etc. These vessels, distributed exceptionally across the shores of Black and Aegean Sea through the mediation of Genoese and Venetians merchants, most probably have inspired the appearance of similar ceramics with Cyrillic monograms and other abbreviations, produced in the inland of Medieval Bulgaria during the course of 14th century and spread mainly in its capital Tarnovo. One of the most important sacred complexes there – the royal Great laura, dedicated to the Holy Forty Martyrs of Sebaste, is the source of an abundant set of inscriptions, engraved underglaze on vessels, used by the monastery brothers in their everyday life. A group of more than 67 plates with the letter “M”, unearthed by the archaeologists, dominate the whole picture. This inscription was first deciphered by At. Popov as the monogram of Bulgarian tsar Michael Shishman (1323-1330), but later was reinterpreted as the number sign for 40 – obviously placed on the vessels to mark them as property of the monastery. It is remarkable that the same practice was noticed in the Serbian monastery of Studenica, where the recent excavations have unearthed some vessels of the same period, marked with the Cyrillic letter “C”. Other vessels with underglaze inscriptions, found in the Tarnovo’s Great Laura, tell us a different story. The engraved personal names are of great interest and historical significance. Among them we should highlight the royal monograms of tsar Ivan Alexander (1331-1371) and tsar Ivan Shishman (1371-1395), and the abbreviated names and titles of the Bulgarian patriarchs Theodosius and Euthymius, known to us from other sites in Tarnovo too. It is still uncertain if they were personal belongings, thus the inscriptions mark property, or they were rather received as gifts by the monastic brotherhood. Other category comprises few liturgical vessels – chalices with Christian formulae. But the most enigmatic of all samples is a plate with a whole Greek-language maledictive text against theft. At this point we can conclude that the Great Laura of the Holy Forty in Tarnovo is a unique example of complex where different types of locally produced Glazed Sgraffito Ceramics with underglaze inscriptions of diverse meaning were used.