When dogs are friendly there are distinct mannerisms you can observe that show they are happy and receptive to meeting you and other dogs. Studying dog gestures and mannerisms is interesting because you learn so much about their personalities, moods, likes and dislikes and whether or not they are friendly or about to attack or become aggressive. Dogs have body language and gestures that are easy to read if you pay attention and observe.
For example, most people think that if dogs are wagging their tails that means they're happy and being friendly. Usually that is the case, but not always. And, it is extremely important to be able to read the difference because it will determine whether a dog is a friend or a foe. When dogs wag their tails straight up and like a flag, very stiff and in short cycles they are actually exhibiting aggressive behavior and are about to attack, especially if they flick their tongues briefly. They are showing signs that they are in fight not flight mode. If their tails are lower, loose and not stiff or vertical, wagging loosely in wide flowing motions then they are happy to see you or meet a new doggie pal. So, watch and learn to make your own observations about the different kinds of tail wagging and what they mean. Notice that when their tails are even with their backs and wagging tentatively that they are unsure and sometimes shy or insecure about the current situation but they are probably more likely to try to flee than fight in that circumstance.
Another misperception about dogs is that they lick when they are happy or showing friendship. Sure, most of the time that is the case. But, like tail wagging there are signs that show some licking is not friendly licking. For example, when they flick their tongues out of the front of their mouths briefly that is a sign that they are about to attack and bite. Also, when they lick compulsively it is a sign of either insecurity or a bit of needy aggressive behavior. They are licking to hang onto you or to dominate you. But most of the time when they are licking you incessantly it means that they adore you and want to clean you out of respect and worship, like they do with the alpha dogs of the pack.
Often times we may think shy dogs are insecure dogs that just need a friendly advance in order to warm them up to us. Be careful with the shy ones! They can often be the most dangerous dogs because they are not giving any warnings that they are about to bite. Dogs almost always warn before they attack or bite with a growl or a sneer- lifting their lips to show their teeth. But with shy dogs sometimes they are so shut down that they are very quiet with very little signs to warn that they are about to bite. So, it is important to pay attention to other signs. Shy dogs will back away or try to retreat. They will hang their heads down low and avoid eye contact or stare at you when they are uncomfortable. Shy dogs bite out of fear. Aggressive dogs bit out of dominance. Both are dangerous and need to be respected.
There are other dog gestures and behaviors that are interesting to observe that show you their nature. Dogs are very territorial and need and respect their individual space. If you watch dogs that share a home or yard or are playing at a dog park, you will notice that they respect each other space and walk around each other's body bubbles. If they want to pass by another dog they will find an alternate route rather than infringe on that dog's personal space. There are those socially inept dogs, just like people, who do not have a clue and barge right through another dog's space but it is rare and will be met with a reaction. Dogs, even the more mild mannered ones, will warn each other with a growl or sneer, to keep their distance or go around another way.
Dogs have a funny way of showing that they really like each other that is completely the opposite as we humans act when we like each other. They do not engage in eye contact. Eye contact for dogs, rather starring is not only rude but a sign of aggression and domination. When they really like each other they do not look at each other and seem to even be ignoring each other. But, when they are hovering around each other and following and playing with each other that means they really like each other. When they ignore each other without any kind of butt sniffing or show of interest then they do not care one way or the other for each other. They are not friend or fool; They are simply strangers who do not have any interest in connecting with each other. Sniffing is their way of showing interest in getting to know each other. If they allow others to sniff them or if they are doing the sniffing that is good social behavior for dogs that want to be friendly and get to know each other. So sniffing should not be discouraged just because we think it is uncouth or obscene because in the dog world it is like our human handshake or hugs.
Dogs are interesting and easy to read and understand if you are paying attention and observing their mannerisms. For the most part, dogs enjoy each other's company and want to get along because that is how best they survive in packs and families. They are happy and social creatures who know life is short so they wag more and bark less!