Drs. Anthony and Crystal Gambino, in their essay on reluctant leadership, look for the following traits:
Some of these characteristics are more fundamental to and may be observed even earlier in the process than Tim Elway’s suggestions. While initiative and passion are somewhat predictable — they’re often the points where we often first notice someone — the others are less obvious.
An interest in being others-focused is an excellent starting point. A willingness to serve and the companion part of it — noticing needs around them — are the foundation of leaders of integrity who support their direct reports. Likewise for a desire to encourage and lift up people around them.
I totally agree with teachability as an early sign of leadership. I’ve heard it said several times that leaders show insatiable curiosity and ask lots of questions. A desire to learn and grow eventually shapes a leader who is a developer of others. Teachability is a trait that can be spotted early and should be part of a leader until the day he dies.