If it wasn’t immediately clear from the trailers filled with props and even archival audio from the original movie, Ghostbusters: Afterlife is stuffed with references and callbacks to the original 1984 Ghostbusters.
(In my review, I compared Afterlife to Leonardo DiCaprio pointing at the TV meme from Once Upon a Time in Hollywood for 125 straight minutes.)
A few, though, are a little bit more obscure and require a [pushes up glasses] deeper knowledge of Ghostbusters lore to spot them.
A lot of the callbacks are obvious; if you’ve ever watched a Ghostbusters you’ll recognize the proton packs and the traps and the jumpsuits.