This character is a Other Symbol and is commonly used, that is, in no specific script.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it is written from left to right. When changing direction it is not mirrored. The word that U+101DF forms with similar adjacent characters prevents a line break inside it.
The Wikipedia has the following information about this codepoint:
The Phaistos Disc or Phaistos Disk is a disk of fired clay from the island of Crete, Greece, possibly from the middle or late Minoan Bronze Age (second millennium BC), bearing a text in an unknown script and language. Its purpose and its original place of manufacture remain disputed. It is now on display at the archaeological museum of Heraklion. The name is sometimes spelled Phaestos or Festos.
The disk was discovered in 1908 by the Italian archaeologist Luigi Pernier during the excavation of the Minoan palace of Phaistos. The disk is about 15Β cm (5.9Β in) in diameter and is covered on each side with a spiral text, consisting of a total of 241 occurrences of 45 distinct signs, which were created by pressing individual sign stamps onto the soft clay before firing. While its unique features initially led some scholars to suspect a forgery or hoax, the disk is now generally accepted by archaeologists as authentic.
This mysterious object captured the imagination of amateur and professional palaeographers, and many attempts have been made to decipher the code behind the disc's signs. While it is not clear that it is a script, most attempted decipherments assume that it is; most additionally assume a syllabary, others an alphabet or logography.