1977 Press Conference The Upcoming Film, "The Wiz"

The simple answer:
The trademark armband that Michael Jackson wears is a symbol of the suffering of children around the world.

Most of his outfits over the past 20 years have featured an armband tied around his right around halfway between the shoulder and the elbow.

Symbolism
1) Most online dictionaries define an armband as: A band worn around the upper arm, often as identification 或者 as a symbol of mourning 或者 protest. A subset of this symbolism is often an element of memorializing innocent victims.

2) Armbands are recognized around the world as a sign of safety and help. they’re commonly worn...