I can't think of many things that are more stupid than having the letter of your fraternity branded on your chest!
It's more common among black fraternities, some seeing it as linking them to their ancestors who may have been branded during slavery, while others simply see it as a way of declaring lifelong devotion to their frat brothers.
I consider it about as silly as frat or sorority tattoos, but then again I have no tattoos or piercings. My father had one USMC tattoo, and so I guess I've seen tats as something you get to express strong devotion...the folks who got cartoon character tats in high school just always seemed silly to me.