An indication would be their empathy towards others, which to me is really important generally. I remember
@Wolfpack bringing up his girlfriends view about ugly people, and this isn't to condemn anyone because he obviously knows a lot more about her than us and see's different sides, but for me, from what he quoted her as saying, these are major warning signals to stay away from someone.
So look out for that. And not just obvious signs of empathy, there's a false moral empathy that people seem to get off on, like everyone feels for a missing child and their family, everyone condemns the actions of paedophiles and murderers, those that tut and bring up constantly how disgusted they are by it, are looking for some "morality points" most of the time. They seek out the most desperate and awful situations so they can express to others how awful they empathise with others, to show how great they are.
Look for empathetic qualities in things that society don't really care about. Caring about the homeless is a start, it's kind of on the fringes though, but as a lot of homeless people are an annoyance and crazy, people say they care about them but in reality it's not really "fashionable". Generally if the other person feels sorry for those who have problems that aren't their fault, acknowledge that, even delve a bit deeper, because it's very important.
That childish cruelty we all had is still inherent and exists in most people, I find. Some are gifted and even lucky to not even feel this, and people like myself are fighting against these cruel thoughts.
