I adopted Sky from the Humane Society and he also has a notch in his left ear. He was brought in as a stray. I thought that he had been in a cat fight but my vet said that they notched his ear on purpose so that he'd be identified as a shelter cat. It must be something new because Storm also came from the Humane Society and he doesn't have any notches in his ears but that was about 61/2 years ago.