There is textual evidence of this throughout the story. One of the most significant instances is Winston's purchase of the old diary in the Prole district of the city.
He had given a quick glance up and down the street and then had slipped inside and bought the book for two dollars fifty. At the time he was not conscious of wanting it for any particular purpose. He had carried it guiltily home in his briefcase. Even with nothing written in it, it was a compromising possession.