Cats have scent glands on their faces, and when they headbutt you, they are marking you with their scent. This is a way of bonding with you. Sometimes, a cat may headbutt you simply because they want some attention. Cats will often present their head in hopes of receiving a head scratching session, so they may try to get you to give them a head scratching. In general, a cat's headbutt is a sign of affection. So if your cat headbutts you, it means they consider you part of their family!