The letter on the bus refers to the event that Kang Youwei and Liang Qichao assembled 1895 in the 21st year of Guangxu in Qing Dynasty, and wrote a letter to Emperor Guangxu, opposing the Qing government defeated in the Sino-Japanese War to sign the treaty of shimonoseki, which humiliated the country.

Because the Han Dynasty used buses and horses to pick up and drop off candidates, then "buses" refers to candidates who went to Beijing to take the exam. The letter on the bus is regarded as a sign that the reformists have stepped onto the historical stage, and also as the beginning of the people's political movement in China.