hook aboveả

A small question-mark-like hook above the vowel, used by Vietnamese alone for the hỏi tone. mả, hỏi, nhỏ, biển, phở. It is one of the five Vietnamese tone marks and can sit on top of a vowel that already carries a breve, circumflex or horn, which is why the alphabet has so many precomposed letters.

Combining mark: U+0309