Here’s a nice little montage of all (or nearly all) of Alfred Hitchcock trademark cameos in his films. By far, his most clever cameo is in the 1944 film Lifeboat, IMO. Just watch.
The films are as follows: The Lodger (1927), Easy Virtue (1928), Blackmail (1929), Murder! (1930), The Man Who Knew Too Much (1934), The 39 Steps (1935), Sabotage (1936), Young and Innocent (1937), The Lady Vanishes (1938), Rebecca (1940), Foreign Correspondent (1940), Mr. & Mrs. Smith (1941), Suspicion (1941), Saboteur (1942), Shadow of a Doubt (1943), Lifeboat (1944), Spellbound (1945), Notorious (1946), The Paradine Case (1947), Rope (1948), Under Capricorn (1949), Stage Fright (1950), Strangers on a Train (1951), I Confess (1953), Dial M for Murder (1954), Rear Window (1954), To Catch A Thief (1955), The Trouble With Harry (1955), The Man Who Knew Too Much (1956), The Wrong Man (1956), Vertigo (1958), North By Northwest (1959), Psycho (1960), The Birds (1963), Marnie (1964), Torn Curtain (1966), Topaz (1969), Frenzy (1972), Family Plot (1976).