An alphabetic letter resembling the colon punctuation mark, ⟨?⟩, is used in a number of languages and phonetic transcription systems, generally for vowel length or tone. 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 ꞉ 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.
Several of the Native American languages of North America use the colon to indicate vowel length. Zuni is one. Other languages include Hupa of California, O'odham of Arizona, Sayula Popoluca of Mexico and Mohawk of Ontario. Still others use a half colon (just the top dot of the colon, or a middot, ꞏ LATIN LETTER SINOLOGICAL DOT). Both conventions derive from Americanist phonetic notation (below).
The colon is used as a grammatical tone letter in Budu in the Democratic Republic of the Congo, in Sabaot in Kenya, in some Grebo in Liberia, and in several languages of Papua New Guinea: Erima, Gizra, Go?bosi, Gwahatike, Kaluli, Kamula, Kasua, Kuni-Boazi and Zimakani.
In Americanist phonetic notation, a colon may be used to indicate vowel length. This convention is somewhat less common than the half-colon.
In the International Phonetic Alphabet, a special triangular colon-like letter is used to indicate that the preceding consonant or vowel is long. Its form is that of two triangles pointing toward each other rather than the two dots of Americanist notation. It is available in Unicode as ː MODIFIER LETTER TRIANGULAR COLON. If the upper triangle is used without the lower one (ˑ MODIFIER LETTER HALF TRIANGULAR COLON), it designates a half-long vowel or consonant.