In the private training session, Katniss Everdeen creates a noose, hangs a practice dummy, and uses the paint to write: Seneca Crane. I know this name is mentioned earlier in the book, but I don't remember who Seneca Crane is... Remind me, please?
Seneca Crane is the previous Gamemaker who decided to allow Peeta and Katniss to live after the berry incident. The Capitol killed her and replaced her for that act of mercy. That's why Katniss hung her; she was rebelling against the Capitol and implying that they murdered Seneca Crane.