Despise one’s father for not being Li Gang

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

The road sign reads, "Friends, slow down a bit; your father is not Li Gang"