1. Alfred Hitchcock made cameo appearances in 39 of his 52 major films. The cameos became a trademark of his films, and a big hit with audiences - who often made a sport of trying to spot him.
2. Eventually Hitchcock made the decision to place the cameos earlier in his films, as to not distract the audience from the plot.
In a 1966 interview Hitchcock said of his cameos:
“I always give a little thought to my appearances and come on as early as possible— don’t want to hold them in suspense for the wrong reason! I’ve been in all my films on and off. Missed a few. Only cancelled one.”