As it happens, today (in some traditions) is the feast day of Saints Cyril and Methodius, who invented the Cyrillic alphabet in the late ninth century. The owner of this apotropaic amulet was presumably an early adopter.
UPDATE: A reader informs me that "the Cyrillic alphabet owes its name to Constantine-Cyril and Methodius, but they are credited with the invention of the Glagolitic alphabet." Thanks for the correction.
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