Pliska 4
Inscription Pliska 4 was incised on a stone from the cornice of the apse of the Palace church. Researchers who found it believe that it is a numerical sign used to mark the stones. Other pieces of the same cornice have similar markings.
Publications:
Абоба-Плиска, Альбом к X тому Извѣстiй рускаго археологическаго института въ Константинополѣ, Вѣна, 1905;