The letter Z is not part of the Vietnamese alphabet, any more than F, J and W. But it is far from uncommon in language use. It appears in the names of companies that target a popular audience, e.g. Zing for a local competitor to Yahoo. Why is Z, the least used letter of the English alphabet, so trendy in present-day Vietnamese? The evidence reported here suggests that the letter Z constitutes foreign-looking clothing for a typical Vietnamese sound. In Hanoi Vietnamese, historical /ð/, /ʒ/ and /r/ (orthographic D, GI and R) merged to /z/, making the voiced alveolar fricative a highly frequent sound – and a potential identity marker for Hanoian speakers, with Z as a unified written rendering. The results of an automated search through a large corpus of contemporary texts support the conclusions drawn from the qualitative analysis of examples.