Why and why does he/she writes "Blood" on the wall?

A man writes 'blood' on the wall in Book the First/ Chapter 5. A wine cask has fallen into the street and broken in the town of Saint Antoine (near Paris). The residents there are destitute and hungry, men are scooping the liquid up into the palms of their hands to drink it, whereas the women are soaking their handkerchiefs the best they can and squeezing the liquid back into the mouths of their children.

In this scene we see the devastation of a people and experience their suffering. The spilt wine their stains their faces, hands and clothing foreshadows the 'blood' to come, as does the word scrawled on the wall. Violence is coming, and the word blood is symbolic of that violence.

Gaspard who is one of the revolutionaries(JACQUES) is the man who wrote BLOOD on the wall and he wrote this because he knows that the revolution is about to come and it might bring turf and turmoil everywhere with violence astounding on the streets.