This is the smooth breathing (psilon pneuma, psili, spiritus lenis) diacritic which was used in Greek to mark the absence of an initial /h/. The diacritic has been adopted into some Latin alphabets as well. There are no precomposed letters with comma above.
Comma Above in Unicode
|Greek Psili||Combining Comma Above|
Comma Above in Natlangs
|Ejective consonant||Heiltsuk-Oowekyala (Heiltsuk dialect, official orthography)||P̓p̓ /pʼ/, T̓t̓ /tʼ/, C̓c̓ /t͡sʼ/, ƛ̓ /t͡ɬʼ/, K̓k̓ /kʼ/, K̓v k̓v /kʼʷ/, Q̓q̓ /qʼ/, Q̓v q̓v /qʼʷ/||The uppercase version of ƛ̓ is an upside down capital barred Y with comma above, but this is not a letter that is included in Unicode. It is unclear if K̓k̓ is palatalized or not. See  and |
|Heiltsuk-Oowekyala (Heiltsuk dialect, Rath's orthography)||P̓p̓ /pʼ/, T̓t̓ /tʼ/, C̓c̓ /t͡sʼ/, T̓h t̓h /t͡ɬʼ/, K̓k̓ /kʼ/, K̓v k̓v /kʼʷ/, Q̓q̓ /qʼ/, Q̓v q̓v /qʼʷ/||It is unclear if K̓k̓ is palatalized or not. See  and .|
|Glottalized phoneme||Heiltsuk-Oowekyala (Heiltsuk dialect, official orthography and Rath's orthography)||A̓a̓ /aˀ/, H̓h̓ /hˀ/, I̓i̓ /iˀ/, L̓l̓ /lˀ/, Ḷ̓ḷ̓ /l̩ˀ/, M̓m̓ /mˀ/, Ṃ̓ṃ̓ /m̩ˀ/, N̓n̓ /nˀ/, Ṇ̓ṇ̓ /n̩ˀ/, U̓u̓ /uˀ/, W̓w̓ /wˀ/, Y̓y̓ /jˀ/||It is unclear what H̓h̓ represents. See  and .|
- Smooth breathing at Wikipedia.
- HAIⱢZAQVLA at Languagegeek.
- Heiltsuk language, Alphabet at Bella Bella Community School.