Often you can tell when a cat is in residence by looking at corners of walls, where two walls meet. There, you will frequently find a little brown cat-height mark, letting you know that it has rubbed its head there repeatedly. Some of my curtains even have such a mark, revealing where one of my cats has brushed the curtain open over and over again to peek outside.
The greasy mark is just residue from natural oils on your cat’s fur. This oil is not really what your cat is interested in depositing. Instead, as the Humane Society of the United States reports, cats have scent glands on their cheeks, their flanks and the pads of their paws. These glands release chemicals called pheromones. Consisting of proteins and other compounds, cat pheromones can trigger the behavior of other kitties.
When your cat rubs its head on walls, furniture, you and anything else, it is therefore leaving behind its own unique scent. Like a signature perfume, this odor helps your cat to mark people, other cats and objects. It’s actually a great honor to be head-rubbed by a cat, because it is informing you that you are very valuable. The same thing happens when your cat kneads its claws on you in a very slow, deliberate fashion. With each move, your cat is intentionally marking you with its scent, again because it values you and may want to return to that same comfy spot again someday soon.
In the wild, such scents are meant to communicate information to other cats. Should another cat come up to your wall or to you, it is then informed that you already belong to another kitty. Sometimes that proves irresistible to other cats that want to claim the desirable people or objects too. At other times, the visiting cat gets the message to back off, since this is a claimed human, cozy couch, soft bed or other desired, pre-discovered possession.