This study adopts an apparent-time diachronic linguistic landscape (LL) approach to investigate the vitality of an ethnic minority language in China, namely the Nuosu Yi ([foreign characters omitted]). Diachronic LL research is concerned with changes in language use on signage over time. It provides insights into phenomena such as language shift, which is challenging to be unveiled through synchronic research. This study collected a total of 1233 signboards, which were made from 2002 to 2021, and thirty follow-up interviews with store owners. By analysing the data statistically and qualitatively, this study demonstrates the changes in language use on private signs of Xichang (the capital city of Liangshan Yi Autonomous Prefecture). A significant finding was a trend for multilingualism, in which the status of Chinese has changed from a monolingual to multilingual dominance, and English has benefited the most from the trend. The use of Nuosu Yi has been high over the two decades, but some issues have arisen with its use on some of the recent-made signs. This study provides a new approach to apparent-time LL research and demonstrates its importance in understanding the dynamic nature of the vitality of ethnic minority languages.