U+1D040 Byzantine Musical Symbol Nana

The Wikipedia has the following information about this codepoint:

Phthora nana (Medieval Greek φθορά νανὰ) is one of the ten modes of the Hagiopolitan Octoechos consisting of 8 diatonic echoi and two additional phthorai. It is used in different traditions of Orthodox chant until today (→ Neobyzantine Octoechos). The name "nana" is taken from the syllables (written in ligatures "ʅʅ") sung during the intonation which precedes a melody composed in this mode. The name "phthora" derived from the verb φθείρω and means "destroy" or "corrupt". It was usually referred to the diatonic genus of the eight mode system and as a sign used in Byzantine chant notation it indicated a "change to another genus" (μεταβολὴ κατὰ γένος), in the particular case of phthora nana a change to the enharmonic genus. Today the "nana" intonation has become the standard name of the third authentic mode which is called "echos tritos" (ἦχος τρίτος) in Greek and "third glas" (третий Гласъ) in Old Church Slavonic.