My old pup, Rusty, recently started exhibiting a new behavior: giving kisses.
I don't encourage him to lick, but when we're sitting all alone and I'm rubbing his chin or cheeks, he'll turn and give me a kiss.
My first impression was that something was wrong, so with flashlight in hand, I went routing around in his mouth to see if maybe he had a cut or abrasion. Nothing.
His appetite is the same, as are all of his biological functions. He's lost a step or two in the last year and a half, but it's been a slow, gradual process, that is probably more closely tied to the time between when we eat and exercise.
It took me a moment, but then I realized that it wasn't something that I was doing, it was his doggie friends. At eighty pounds and a bounce in his step, you either love him or fear him if you're a smaller dog. Luckily the overwhelming majority love him. Those that don't are either kept well away by their owners, or bark like crazy enough that Rusty gets the hint to steer clear.
The many dogs that love him are smaller and will happily come over to say "Hi" and jump up and lick his face, which experts will tell you is a sign of submission or respect. Even the more shy or nervous dogs calm down given a chance to get close enough. There have been a couple of incidents where one dog or the other will get anxious and both will get mouthy, but that is much more the except than the rule in my case. If you're going to socialize any dog, I'd recommend making sure that they're calm, happy, and know how to tolerate others without having to be in their face first.
On the other side of the fence, we've come across more young, energetic dogs, that calm down in his presence as if understanding that it's not necessary to get crazy with every dog they meet. There are usually plenty of wags to be had on either side with my older guy occasionally joining the play session to let the younger crowd know that he's still a pup at heart.