I believe they do this because they see us as teachers, not individuals. When the year begins, I identify them quickly and purposely seek them out for casual conversations. Mostly, this is at sporting events, lunchtime, in the hall and when I see them in the community. They begin to see me as an individual who is interested in their lives, not just a teacher. I rarely need to send students to the principal and the teaching and learning process can continue without interruption.
Doctors do it.
I'm talking about prominently displaying educational degrees and professional certificates. Displaying one's credentials will help you appear professional and legitimate. It's very impressive and reinforces to the public the amount of effort it takes to become a teacher and to maintain certification. Sometimes students have insight that teachers forget to consider. Their comments help me improve my lessons and teaching techniques as well as see myself through their eyes.