They talk to their children in a polite, loving way, even when they're tired and frustrated.

They don't tell you they are a good person

Treating service staff as human beings is the no.1 indicator for me. Which is so depressing when you think about it.

The most subtle sign is catching them during a moment when they think no one is watching. That’s why the cart return thing is definitely telling of you as a person.

They respond with curiosity rather than anger.

They’re helpful without bragging about it. They’re generous without asking for generosity in return. They’re kind to people they don’t know.

Casually considerate. They open doors for people without thinking; they ask if anyone wants anything if they're grabbing snacks/lunch/getting off the couch; they don't play a game of chicken with people trying to merge into traffic and instead just let people over; if someone drops something, they pick it up and give it back; they notice if someone is upset and ask if everything is ok; etc, etc. Has to be consistent behavior and occurs for anyone, not just, say, attractive people.

Holding onto trash until they find a trashcan.

They call you when they're going to be late instead of leaving you twisting in the wind.

Treats people with no power with dignity and respect.

When someone includes everyone in a conversation.

They say nice things about others behind their backs.

If you catch them secretly doing something generous, that's usually something only a person with honorable motives will do.

Genuinely happy when good things happen to other people, even when they don’t ‘get’ why it’s a good thing or if it was something they also wanted.

Honestly, in my experience, people who are worried that they might be bad are people with good intentions. If they were not a good person, they wouldn’t care if they might be a bad person.

I have a friend who is really good at acknowledging when people speak. So when we’re in a group and people naturally might cut someone off just by nature of the conversation, they do an amazing job at redirecting the conversation to ask what it was you wanted to say to ensure no one gets ignored or feels left out.