YSK: touching a cat's belly often means "play" to them, so expect to possibly be scratched.
For most cats, the proper way to pet a cat is to let it sniff or rub against you first, then give it some pets on the head or by the cheekbones, or for some cats along the back, or for some cats "bongos" by the tail. But if you pet their belly, they see that as playing, so that can often lead to getting scratched. That does not mean that they dislike you, but rather they think you are trying to play with them. While it is true that some cats are into belly rubs, if you do not know the cat, be cautious rubbing their belly.
Why YSK: a lot of people do not know how to pet cats, and so they get scratched or they assume that cats dislike them #education