a special double-triangle colon symbol is used in ipa to indicate that the preceding sound is long. its form is that of two triangles, each a bit larger than a point of a standard colon, pointing toward each other. it is available in unicode as modifier letter triangular colon, unicode u+02d0 (). a regular colon is often used as a fallback when this character is not available, or in the practical orthography of some languages (particularly in mexico), which have a phonemic long/short distinction in vowels.