Does anyone have good resources for information on this subject?

I have a character who needs to be marked that he was sold into slavery young (around age 10), and another character who discovers his scars later in life when he's about 25. So I'm curious about different methods of achieving this, and how the appearance of the affected skin would change over time, specifically because the character being scarred moves from childhood to adulthood.

For story purposes, it would be nice if I could find a way to make it credible if the mark were about palm-sized. Branding was the first thing that came to mind.