Hmmm. As a young person who appreciates body modification, I also thought it was unusual when I first came across the whole branding thing, but this response is based on pre-conceptions, lack of knowledge, and a tendency for people to prefer judging rather than even attempting to understand things. There are three things I would like to point out:
1. Branding(I am sure there is a proper name for it, but I cannot remember what) when correctly and safely done in a licensed tattoo/piercing studio is a legitimate form of body modification. It may appear strange to you, after all tattoos don't make sense to many people, but it is legitimate.
2. It is nothing to do with self-harm. There are self-harmers who end up with visible scar tissue, but someone who brands themself like we are talking about is doing this to get the design on their skin, not because they feel they need the sensation that branding themself will bring. Self-harmers cut themself to actually experience the sensation of cutting, people with legitimate brandings do not. According to the reasoning above, people with pierced ears are self-harmers.
3. Branding yourself in your bedroom with a coat hanger is NOT the legitimate and safe branding I have discussed above. It's a bunch of foolish kids trying to get the effect cheaply and dangerously.