One way a cat communicates their mood is with their tail. When the tail is held straight up, it expresses confidence. When your cat wraps it's tail around your legs, it communicates friendliness. If it is tucked between their legs, it signals anxiety.
So, when you come home from a long day at work and your cat rubs up against you and wraps their tail around your legs, that's their way of saying "I missed you!"
When felines interact, responding with a slow blink is an official sign of trust. Like a wink between friends, your cat may close their eyes in your presence to show that they are friendly and comfortable with you. It is a signal of acceptance that a cat may only communicate with their owner.
Cats develop a vocal language that is unique to them and their owner. Your cat may meow as a way of greeting you, requesting food, or asking for approval. Purring is also a way for your cat to communicate with you. Purring is a sign that your cat wants to be comforted and/or cared for. Pay attention to the different sounds your cat makes, so you can better understand their specific way of speaking to you.
Source: DailyMail, nymag, webmd, huffingtonpost