No Ghosts

In this secret, the anonymous sender is, or claims to be, a "spiritual medium". These people have often been the focus of controversy because of the nature of their work. This sender completely exposes themselves and other mediums as fakes and liars. This is an explicit claim. What is implied here is that people should stop believing these "mediums" and stop wasting their time on someone who will lie to them.
The sender wants the whole world to know about his/her experiences as a liar/spiritual medium. The intended audience is anyone who has ever questioned the authenticity of such "professionals."
The photo in the background is a ouija board, which is supposed to allow the user to tap into supernatural energy to answer questions or communicate with dead. This is an extremely appropriate background since most people regard the ouija board to be child's play. What the sender did was equate the profession of these "mediums" to a child's board game.