It’s a joke. It’s a screen grab from George Romero’s 1978 classic Dawn of the Dead, where survivors hold up in a mall that is over ran by zombies, hence “dead mall”.
No problem, and if you haven’t seen it, check it out. Great film, but if older films aren’t your fancy, the 2004 remake of the same name holds it own as well. It’s directed by Zack Snyder.