Davis Okoye (Dwayne Johnson) signs to Pablo to calm the gorilla down, signing "It's me." The sign he makes is for "rock," a reference to Dwayne Johnson's nickname "The Rock."
George was originally intended to be a regular gorilla until the filmmakers and creature designers made the decision to make him an albino gorilla due to the fact that it would allow the damage done to him to be more visible and to make him stand out and not just another "King Kong rip off".
Both George, the gorilla, and Ralph (the wolf) share their names with their video-game counter-part. The crocodile, who is called Lizzie in the game series, never has its name mentioned.
The mutated rat seen towards the beginning of the film is likely meant to be Larry from the Atari Lynx version of Rampage (1986). The character was a special inclusion who only appeared in this version of the game.
An original cabinet of the Rampage arcade game can be seen in Claire Wyden's office.