A rule in prisons, though I know it has become more of an issue in all schools, is “no touching is the best policy”. It is a prison rule all inmates know, and it can lead to a write-up for them. They cannot touch any of the staff.
Occasionally, I have given a professional handshake. When a man is on his way to be released and he is thanking me for helping him pass his GED, or he is thanking me for being his teacher, or coming to say goodbye, I will shake his hand.