Pickwick; 'but old men may come here through their own heedlessness and unsuspicion
, and young men may be brought here by the selfishness of those they serve.
Whether the shadow-casting obstruction is comprised of slatted blinds, lathed stair balusters, or a window with a private investigator's name painted on it, the striking depiction of light having passed through to "X" is wholly consistent with the aura of unsuspicion I view as both noir's narrative core and its key generic difference.
This fantasy of unsuspicion correlates closely with a parallel 1940s discourse concerning the pre-emptive power of medical X-rays: the notion that the apparently healthy exterior views people take for granted are the ones they should most acutely suspect.
Nowhere in film noir is the conceit of X-ray vision, and its impossibility in human terms, given a more literal treatment than in the noir amnesia plot, a scenario in which the public's passive unsuspicion is reconfigured as an active quest.
As such, film noir does not seek to raise public awareness about the prevalence of modern crime or the need for skilled detection, but rather to cultivate an awareness of unsuspicion itself.
My thanks to Todd McGowan for suggesting this very useful way to conceive the topology of unsuspicion in noir.