Cats rub against things to put their scent on it. It's a way of saying "This is mine."

1) "Some cats will rub their faces along their guardian's cheek or ankles as a friendly greeting or sign of affection. This action is also sometimes a way of "marking their territory," leaving a scent from the scent glands located in the cat's cheek." Source and further information: http://en.wikipedia.org/wiki/Cat_communication 2) "For instance, a cat rubbing its body along an arm or leg of its human is not only a way in which to attract attention and, perhaps, a morsel of food; it is also a way of 'marking' its human as its own. Using scent glands located around its mouth and elsewhere, it subtly 'marks' its human as part of its cat territory. Most cats prefer gentle rubs behind the ears. To inform their humans they need petting or attention, a cat may push its entire body weight up against the human as the cat snuggles next to his/her favourite person." Source and further information: http://en.wikipedia.org/wiki/Cat_body_language 3) "Scent Rubbing This behaviour is used primarily to claim ownership of something: although female cats don't spray, unlike male cats. Once male cats are neutered the scent rubbing or spraying will wear out or stop." Source and further information: http://en.wikipedia.org/wiki/Cat_behavior