What is the meaning of ꞉?

Alternative form of ꞏ for vowel length (e.g. ⟨a꞉⟩).

A component of the vowel letters ⟨a꞉⟩ and ⟨o꞉⟩ in a number of languages Papua New Guinea (e.g. Gobasi ⟨Go꞉bosi⟩).

The grammatical tone marking past tense.

Found in the Cayuga letters a꞉ e꞉ ę꞉ i꞉ o꞉ ǫ꞉.

A marker of long vowels and geminate consonants in the Halkomelem alphabet.

the palatal click, modern ⟨ǂ⟩ (Besides the single letter, ⟨꞉⟩ is also used in digraphs for the palatal click consonants ⟨꞉k ꞉g ꞉n ꞉h ꞉kh ꞉ch⟩.)

A mark of vowel length in the Kiowa alphabet.

A letter for vowel length in the Boazi alphabet.

Low lexical tone, on a syllable ending in a vowel or in any consonant but glottal stop.

The grammatical tone that marks a subject.

Marks long vowels: a꞉ ä꞉ e꞉ ë꞉ i꞉ o꞉ ö꞉.

Marks nasal vowels.

Source: wiktionary.org