9:29 second in to the movie the word 'Doom' is spray painted on the window and can be clearly seen. This is also a first person shooter!!
One of few zombie movies to actually refer to them as 'zombies'.
In the school scene (at around 37 mins) there's a QR code at the door that reads the website from Ramona Convent, a school in Alhambra, CA, probably where the scene was filmed.