This is Annie. A Rhodesian Ridgeback mix, and a rescue. She is happy to see me and is smiling! She is not baring her teeth in aggression. This is a form of submission amongst many dogs – and is unique to the dog. Some breeds may smile more than others, but not all dogs will perform this act.
If a dog you are not familiar with bares it’s teeth in such a manner, best to lean towards the side of caution and not assume the dog is smiling in submission.