In typesetting, the hook above (Vietnamese: dấu hỏi) is a diacritic mark placed on top of vowels in the Vietnamese alphabet. In shape it looks like a tiny question mark without the dot underneath. For example, a capital A with a hook is "Ả", and a lower case "u" with a hook is "ủ". The hook is usually written to the right of the circumflex in conventional Vietnamese orthography. If Vietnamese characters are unavailable, it is often replaced by a question mark after the vowel (VIQR encoding).
This diacritic functions as a tone marker, indicating a "mid falling" tone (hỏi): which is "dipping" (˨˩˥) in Southern Vietnamese or "falling" (˧˩) in Northern Vietnamese; see Vietnamese language § Regional variation: Tones. The Southern "dipping" tone is similar to the questioning intonation in English.