The aim of this paper is to elucidate a pragmatic use of imagination, focusing on that of the political police to detect latent complaint in wartime Japan. Public scribblings, collected and recorded by the police, provide a good instantiation. During the war (1931-45), they took care of them as anti-establishment political thought, and collected them in the Tokko Geppo, a monthly secret report about the social movements. At the same time, they treated them as the representation of latent complaint in the society, having nothing to do with the Left. Therefore, these documents had two aspects: 1) thought control and its crackdown, 2) research about the society the police were sworn to protect. To attain both goals, the police developed their imagination based on the memory of city riot in the Taisho era. From fragmentary graffiti, they imagined the disturbances which might grow up into riot behind the calm society under their powerful control. These compilations are the vestige of police's method to comprehend their contemporary society.