Head bumping is a display of affection, insofar as what we humans understand as affection. Cats are loaded with scent glands, around their ears, cheeks, tail, etc. All that rubbing that they do all over the house is marking what is theirs; sofas, doorways, people's legs, etc.

That may not be a very flattering description of what's going on, but take heart. You happen to one of the things that your cat likes and wants to claim. Be flattered. They can be finicky characters, so it is a compliment.

Some interesting studies have been done with animal emotions. Pet scans of the human brain have been mapped so we know which areas of the brain light up for given emotions. Interestingly, scans have also been done on dog and cat brains, and sure enough, the same areas light up for the same emotional displays. So you can be assured that your pet feels the same emotions (fear, anger, affection) that humans do. And their intelligence levels rank somewhat similar to toddlers. Makes a person rethink how we as a species treat the animals we share the earth with.