Thought impressions are embedded memories of thoughts connected to a specific object, usually objects with writing on them.
A small number of Psys are capable of picking up the thought impressions on writing left by readers. It is unconfirmed as to whether other objects can be "read". Reading specific thought impressions is made more difficult when more different thoughts are impressed into an object, and thought impressions may be reinforced the more a thought is impressed (e.g.: through words being read multiple times)