The term 'MYSTERIOUS, AS SOME OLD INSCRIPTIONS' can be summarized by the crossword solution 'RUNIC, ' which refers to a type of writing system used by Germanic and Scandinavian peoples from the first century CE to the Middle Ages. Runic inscriptions were often found on jewelry, weapons, tools, and other objects, and were used to convey messages or record events. These inscriptions are often mysterious and difficult to interpret, making them a source of fascination for many.