Transcription
In the International Phonetic Alphabet, labialization of velar consonants is indicated with a raised w modifier (Unicode U+02B7), as in /kʷ/. (Elsewhere this diacritic generally indicates simultaneous labialization and velarization.) There are also diacritics, respectively, to indicate greater or lesser degrees of rounding. These are normally used with vowels, but may occur with consonants. For example, in the Athabaskan language Hupa, voiceless velar fricatives distinguish three degrees of labialization, transcribed either /x/, /x̹/, /xʷ/ or /x/, /x̜ʷ/, /xʷ/.
The Extensions to the IPA has two additional symbols for degrees of rounding: Spread /ɹ͍/ and open-rounded /ʒœ/. It also has a symbol for labialdentalized sounds, /tʋ/.
If precision is desired, the Abkhaz and Ubykh articulations may be transcribed with the appropriate fricative or trill raised as a diacritic:, .
For simple labialization, Ladefoged & Maddieson (1996) resurrected an old IPA symbol, . However, their chief example is Shona sv and zv, which they transcribe /s̫/ and /z̫/ but which actually seem to be whistled sibilants, without necessarily being labialized. The open rounding of English /ʃ/ is also unvelarized.
Read more about this topic: Labialization