“You must register” is something a guard in the game X-Wing says if you try to play without selecting a username. He says it in a Schwarzzenager-esque voice. It’s funny.
My brothers and I used to try playing without entering a username over and over just to hear him repeat it. Sometimes the game’s audio would overlap as we rapid-clicked to cue the statement, and he would stutter “You must— You must— You mus— You— You must register.”