The colon alphabetic letter ꞉ is used in a number of languages and phonetic transcription systems, for vowel length in Americanist Phonetic Notation, for the vowels ⟨a꞉⟩ [ɛ] and ⟨o꞉⟩ [ɔ] in a number of languages of Delhi, India, and for grammatical tone in several languages of Africa. It resembles but differs from the colon punctuation mark, :. In some fonts, the two dots are placed a bit closer together than those of the punctuation colon so that the two characters are visually distinct. In Unicode it has been assigned the code U+A789 ꞉ MODIFIER LETTER COLON, which behaves like a letter rather than a punctuation mark in electronic texts. In practice, however, an ASCII colon is frequently used for the letter.
In Windows and macOS, the letter colon can be used to emulate the punctuation colon in file names, where the punctuation colon is a reserved character that cannot be used.