It is a sign of appeasment to the leader of the pack. The top dog in my pack, Bouncer, has three of my other males hanging around, licking his face/mouth. Also, in the wild, it signals the mom to regurgitate food for the pups. lol Gross I know.
My Zeus always licks our faces! You should have seen him when we mt this gorgeous male longhaired chihuahua who literally looked like a little lion he was killing him with kisses!! lol!! I didn't know about the mother thing tough!! QAnd YES that is gross ha ha!!