Calming signals is a term coined by Turid Rugaas to describe a behavioral language that dogs use to communicate with their own kind. People who take the time and effort to learn and understand the meaning behind calming signals can also learn how to communicate and understand their dog's behavior in a more reality based way.
Learn how to recognize and interpret the main signals -- lip licking, turning away, yawning, sniffing -- by reading up on their meaning, taking a class with a professional who helps interpret signals in both on and off leash circumstances and by all means, watch dogs.
You can watch dogs in your own home, in your neighborhood, in dog class, at pet stores or other common gathering places for dogs (dog parks, on sidewalks, hiking in nature, vet offices, groomers, etc.) You can watch dogs on T.V.
While calming signals convey stress, not all stress is bad. A signal is communicating how the dog feels and it can literally change from instant to instant, snap, if things are active, at least from the dog's perspective!
Next time you feel your dog is riled up, challenge everyone around to ignore the dog, sit and stretch and yawn, slowly, and watch what happens.