I look for signs that the person is interested in what they are doing. Private projects with public repositories are a sign but nowadays I see people started showing up who force themselves to do these projects just to improve their interview prospects.
I even had one person admit it when it was obvious they can't tell me anything about their own project.
Obviously, this is a result of a very know effect where judging performance based on some measurements causes people to pervert this measurement.
Other signs that people overlook and misunderstand is deep knowledge on any topic related to software development. If somebody could acquire good, deep understanding of at least one topic it shows they were likely at least at some point interested in it.
People are sometimes put off that I seem to be asking large number of hard questions and then grilling to death, but that's what I am doing, looking for signs of being interested in something.
I even have one question where I ask: What is the question you would like me to ask you? That's just another occasion to have a discussion on something where the candidate can demonstrate their deep knowledge.