Never forget the national humiliation; revive China.
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Classical / literary. 毋 (wú) is a literary negative ('do not'), the colloquial equivalent being 不要 (bùyào). You'll see 毋忘 mostly on monuments, slogans (毋忘国耻), and inscriptions.
history
毋忘在莒 (wúwàng zài Jǔ) is a classical four-character phrase meaning 'don't forget your hard times in Ju' - Chiang Kai-shek invoked it after retreating to Taiwan, making it a politically charged expression.
