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 or as a symbol of mourning or 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 by medical personnel in the field, the most well known being the Red Cross armband. The Red Cross notes: “The familiar arm band symbol and Red Cross name tag signify someone you can trust, someone you can turn to.”

3) The 3rd most common use of the armband is to show prominence, leadership, achievement or honor – from Nazi and military/militia usages throughout history, to parade marshals, to the armbands worn by Thai boxers

Michael Jackson doesn’t wear armbands because he’s having fun with fashion. he’s wears this specific item of clothing every day of his trail because it carries strong psychological and cultural associations, and he's trying to subliminally convey to the jurors a message: protest of his victimization, and that he is a prominent person of honor that can be trusted.