They're self aware. Understand the difference between subjectivity and objectivity. When they encounter someone different, they don't judge, see it as a learning opportunity. Put thought into their words. If you ask them a question, you can see them carefully thinking about it.
Everyone judges, it's how you act upon that judgement that is the mark of your character. Anyone that says "I don't judge" is either full of shit or means that they are self aware of their biases, conscious and subconscious and don't act upon their judgements.
Judging people is a natural part of being human and impossible to not do.
I would just append that judging people is a good thing, often blanket misinterpreted as a bad thing. You should make an initial judgement upon meeting someone (it doesn't really matter, your subconscious will anyway). The important part is being willing to update that judgement based on learning more.
I've spoken about this with my girlfriend. She mentioned that we shouldn't judge a book by its cover and I get what she was trying to say but everyone judges and to a certain extent everyone should judge. It's how you act upon that initial judgment and your willingness to append it that shows your character.