A gob stamp is a symbol of the Rogers High School in (Puyallup, WA) "gang" called the Gobs. It's a cigarette burn mark on the hand to permanently brand you as a Gob. It's mostly done to make them seem super ~edgy~. But it's just gonna leave a gross scar that no one is going to care about two years from now.
Girl: Hey, what's that on your hand?
Boy: Gob stamp bro. GOBS4LYFE