His contribution to the auteur theory centers on his notion of the caméra-stylo or “camera-pen” and the idea that directors should wield their cameras like writers use their pens. 

(source – https://en.wikipedia.org/wiki/Alexandre_Astruc) 

EXAMPLES: 

(Alfred Hitchcock) 

(Psycho (1960)) 

(Vertigo (1958)) 

(Rear Window (1954)) 

(signature use of light/shadows and close ups of characters when there is a suspicious or ominous atmosphere)