Surprisingly it isn't Superman, contrary to Batman v Superman's focus on their fear and apprehension towards the Man of Steel. A newspaper can be spotted in Freddie Freeman's room in the Shazam! trailer, which features the main headline "Superman Is Back". If you look down below the image of his symbol you'll find another article with the headline "Amazon Woman And The Batman Help Combat Lex Luthor Plans."
The text underneath that headline is even more interesting, displaying that citizens aren't the only ones pegging the blame on Luthor for the attacks. It reads "The Top Suspect: As a worldwide search begins for those responsible, specialists say early signs point to Lex Luthor and his associates."
The associates part is interesting too, as it either is referring to Steppenwolf and his horde of Parademons (unlikely) or associates like Deathstroke, who fans glimpsed at the end of Justice League. That scene also hinted that Luthor was starting his Legion of Doom, so was his pitch to Deathstroke just one in a long line of them or was that truly the beginning? Hopefully, there's a Justice League sequel so we can all find out.
You can check out the newspaper in question above.
Shazam! is directed by David F. Sandberg and stars Zachary Levi (Shazam), Mark Strong (Dr. Thaddeus Sivana), Djimon Hounsou (The Wizard), Jack Dylan Grazer (Freddy Freeman), Asher Angel (Billy Batson), Grace Fulton (Mary Bromfield), Ross Butler, Adam Brody, and Michelle Borth.
"We all have a superhero inside us, it just takes a bit of magic to bring it out. In Billy Batson's (Angel) case, by shouting out one word—SHAZAM!—this streetwise 14-year-old foster kid can turn into the adult Super Hero Shazam (Levi), courtesy of an ancient wizard. Still a kid at heart—inside a ripped, godlike body—Shazam revels in this adult version of himself by doing what any teen would do with superpowers: have fun with them! Can he fly? Does he have X-ray vision? Can he shoot lightning out of his hands? Can he skip his social studies test? Shazam sets out to test the limits of his abilities with the joyful recklessness of a child. But he'll need to master these powers quickly in order to fight the deadly forces of evil controlled by Dr. Thaddeus Sivana (Strong)."
Next up for DC is Aquaman, which lands in theaters on December 21st. Shazam! is slated to hit theaters on April 5, 2019, while Wonder Woman 2 hits theaters on November 1, 2019.