In the Smallville episode where Lana's ex, now a Marine, supposedly "returns" (although, in fact, he's dead), he marches down the hall of the school in the very beginning wearing his uniform. His rank insignia is that of a PFC (Private First Class), but his trousers have a Bloodstripe (red) on them. Only NCO's (Non-Commissioned Officers) and above are qualified to wear the Bloodstripe.