Ears

When a dog is relaxed, the ears might be down, but its ears might become erect and stand up when a dog is alert. If a dog feels threatened, the ears do go up. It also happens due to aggression. You might be able to see your dog’s ears up when they think they hear something. Sometimes one ear might be up. Other times both the ears might be up.
Raised Hair

Sometimes, the hair on the back of your dog’s back/neck may rise. This can be a sign of aggression when they are fighting with other dogs. However, it might not always be for something negative. It can be the same way people get goosebumps; dogs have hair that rises on their back and upper shoulders.
Posture

Posture is very important in people, and it is important in dogs as well. If a dog cowers in a corner, it could mean that the dog is scared. If he looks fully puffed up and upright, he might be trying to look bigger and aggressive. A dog may roll over to show they are submissive or want to get a belly rub.
Eyes

Dog’s eyes can be important in understanding how they feel. If they stare at you hard, then it could mean that they feel some threat. If your dog is stressed, then it may simply avoid looking at you. This is not your dog ignoring you. It could simply mean that your pet feels stressed. If you feel your dog is not comfortable, you can pat him a little and play with him or give him a bone. If you show him some love, he will be happy soon.
Conclusion
It would be best if you tried to look at all these signs because many of them might happen together. All the signs fit together to show you how the dog feels. Do not provoke any dog because even though they look cute, they can be vicious if you threaten them or the ones they love. You must understand the signs that your pet gives you because it will allow you to communicate better and understand your pet. You will develop a good bond with your pet if you understand them, and it will make you closer.