What does the signpost mean?

This stone is called a milestone. It says so-and-so road, which means that this line is called so-and-so road, and it is generally marked with "G123" (G stands for national highway, and provincial highway is marked with S; 123 is a number, and the numbers of different lines are different), and at the same time, it is marked with "so-and-so line" (for example, "Shanghai-Hangzhou line" means Shanghai to Hangzhou). The following figures are the total kilometers from the starting point to this milestone. "1" means that the starting point is exactly 1 km.