What does it mean when a cat sniffs your face?
It is the equivalent of touching the hand of your partner or spouse. It is your cat making contact with your through your natural body scent. For your cat it is a confirmation of your presence. Perhaps too it provides your cat with a reassurance that you are you and not someone else. This is an interspecies friendship. We all know by now that cats rely on their sense of smell a lot more than humans. It is like another pair of eyes for a cat.
Cats will also sniff the nose to smell your breath. It is all about the power of body scents – so important for cats.

Cat sniffs face
Whereas a loving husband might touch his wife gently on the shoulder or give her a little kiss as he passes her to reassure her and tell her that he loves her, a cat will smell your face and perhaps follow it up with a lick. Same difference 😉
In answer to the question, it does not mean anything. It is not meant to mean something. This feline behaviour serves a purpose as described.
That is my take on why a cat sniffs your face. I have not read anything on this. I have not checked for any studies because there won’t be any. I have simply thought about it briefly and presented those thoughts here. You may disagree and have a better reason. I’d love to hear it.
Happy Christmas to all visitors. I appreciate your patronage.