Rope (1948) - Hitchcock's cameo
Hitchcock's cameo in Rope (1948) occurs about 55 minutes into the film, where he appears in the background as a red flashing neon sign of his trademark profile.
Several newspapers reported on the cameo during the film's production, including the Yorkshire Evening Post (07/Feb/1948):
According to an in-depth article on the film by American Cinematographer editor George E. Turner, the sign was supposed to represent The Reduco Corporation, manufacturer of the "Obesity Slayer" which formed Hitchcock's cameo in Lifeboat (1944).
As the sky darkens, lights begin appearing in the windows of the buildings and neon signs flash on. One of these signs depicts before‑and‑after figures advertising a product called Reduco. The model for this was the director, whose portly figure is well known, making the token personal appearance that had been a tradition in his films since The Lodger, made in 1926. He had used the Reduco gag as a newspaper ad in Lifeboat (1943), another one‑set show in which he could not logically do a walk‑on.
This was also confirmed by a brief comment made by Hitchcock in his 1948 article, "My Most Exciting Picture":
In a report on the director's planned appearance in Rear Window (1954), the New York Times (03/Jan/1954) summarised a few of Hitchcock's other cameos, including that he "appeared on a neon sign carrying the legend 'Reduco' in Rope."
Some sources claim that Hitchcock has an initial cameo in Rope as the man walking down the street during the opening credit sequence and the individual does resemble the director. However, in the The Encyclopedia of Alfred Hitchcock, Thomas M. Leitch states that the production records in the Warner Bros. archive show that the neon sign is Hitchcock's only appearance in the entire film.