Alfred Hitchcock made cameo "innocent bystander" appearances in nearly all of his films. He placed them in first few minutes of the movie so audiences wouldn't be distracted from the story while they were watching for him to pop up. Here is a helpful guide to where you can see all of the cameos. One hint when trying to find them while watching a movie ... put down the popcorn and pay attention, they go by quickly!
Approx. Timestamp: 0:40
In silhouette through the a door.
Approx. Timestamp: 0:03
Part of a crowd shot.
Approx. Timestamp: 0:33
Being pushed in a wheelchair at an airport.
Approx. Timestamp: 0:08
Sitting in a hotel lobby with a baby on his lap.
Approx. Timestamp: 0:05
Entering from the left of a hallway after Tippi Hedren passes by.
Approx. Timestamp: 0:02
Leaving the pet shop with two dogs.
Outside Janet Leigh's office window wearing a cowboy hat.
North by Northwest
Right at the beginning of the movie, just after his name disappears on screen.
Walking in the street wearing a grey suit.