Scrum Masters are true leaders who serve the Scrum Team and the larger organization. - Scrum Guide.
A True Leader may exhibit characteristics such as:
Leads by Example: Scrum Master not only invites the team members to regularly seek feedback and try to continuously improve, however, models exhibiting the same and seeks feedback about their own performance and strives to keep improving how they serve the team, the product owner and the organization.
Supports those having difficult times: The Scrum Master stands in support of those who are having difficult times. Team members having difficult times don't need to be treated as bad people. The Scrum Master emphatizes and stands in support of these people.
Leads by Serving: Not there to Manage, the Scrum Master serves to lead.
Also see: Scrum Master as a Servant-Leader