Despise one’s father for not being Li Gang
From China Digital Space
恨爹不成刚 (hèn dié bù chéng gāng): Despise one’s father for not being [Li] Gang
This phrase sounds almost the same as the Chinese idiom, “despise iron for not being steel” (恨铁不成钢 hèn tiě bù chéng gāng). That idiom is used to express disapproval of someone’s lack of progression and a hope that they will improve.
The variant, “despise one’s father for not being [Li] Gang,” refers to the Li Gang Incident in which a young driver attempted to shirk responsibility for killing a pedestrian by invoking the government position of his father. The phrase is used to ask rhetorically, "Why was I not born to a privileged family?" "Why can't I escape the legal consequences of my actions?"
The road sign reads, "Friends, slow down a bit; your father is not Li Gang."