A clipping of the famous chengyu
替天行道 (tì tiān xíng dào, 'on behalf of Heaven, carry out the Way') — the rallying cry of the 108 outlaws in 《
水浒传》 (Shuǐhǔ Zhuàn, Outlaws of the Marsh / Water Margin). The phrase justifies rebellion against a corrupt government as Heaven-sanctioned.