It might be a YA sci-fi book.
The teens had metal letters/numbers embedded in their heads and might be gang members.
There might be a prison on the moon.
I know it was published before 1987. I read it at the Morley Public Library in Painesville, Ohio in 1986. It was written in English.
Possible 'Exiles of Colsec' and sequels by Douglas Hill. Two of the protagonists (Jeko and Rontal) are gang members with a metal 'S' on the forehead and their initials raised scars on their heads.
In the last novel, they escape from a prison and fight a battle within an asteroid mine.