And those are often times referred to as "Easter Eggs"..just cool little things the people slip in that has some kind of meaning to them.
What does it mean Easter eggs in movies?
Easter egg (media) is a term used to describe a message, image or feature hidden in a video game, film, or other that's usually an electronic medium. It's those little sneaky hidden messages in your favourite film that you love to spot and makes you go “ahhhh, clever!”.