Hard to tell. In many cases, there may be no real outward signs. In other cases, a person may talk to themselves or even gesture to themselves as if they are having a conversation with an imaginary person. In other cases, a person may display signs of paranoia, such as barricading themselves in their room, calling the police complaining that others are out to get them, as well as certain other behaviors.
Thoughts and Voices. The two most classic symptoms of schizophrenia are delusions and hallucinations. Delusions are bizarre false beliefs that are rigid held despite overwhelming evidence to the contrary. Hallucniations are sensory perceptions in the absence of a stiumlus in the environment. The usual example is hearing voices or seeing people when no one is there.