I’ve found your cap

Len was thirty years old, and he had very long hair. He lived in a big city, but one year he did not find any work there, so he went to a small town and began looking for work there. He went to a lot of places, but nobody wanted him.
Then he met an old friend, and this man said to him, “People in this town don’t like long hair. Why don’t you go to a barber? He can cut a lot of it off, and then you can get some work.”
Len went to a barber and said, “Please cut most of my hair off.”
The barber began. He cut and cut for a long time and then he said to Len, “Were you in the army a few years ago?”
“Yes, I was,” Len answered. “Why did you ask that?”
“Because I’ve found your cap,” the barber answered.

Could you tell me what the barber means by "I've found your cap"?