Sealed with a lick.

Dog kisses are like eating oysters; a little messy, often gamey, and not for everyone. But most dog lovers put up with it because they know how much joy pooches get from licking people's faces like they were bacon-flavored and smothered in gravy. Dogs can't express themselves with words, and tail-wagging is involuntary, and usually means they're happy to see you. But a good face-licking is a dog's way of saying, "I love you," and it means a lot to them that you accept their sloppy affection. Just try not to dwell on the fact that may have just said "I love you" to their ass and balls.

Sources: Laughing Squid