Adventure Time in The Division
Characters from this series can be found as graffiti on a wall in Pennsylvania Plaza (about 850/1188). The mural extends quite far, making it worth taking a look if you are a fan of Adventure Time.
Doctor Who in The Division
Whether this is really an Easter egg is controversial, as a connection to Doctor Who seems a bit far-fetched. In one episode, there were “killer mannequins”, a scene that is presumably being reenacted here. You can find the mannequins in the basement during the Lexington Event Center mission. However, the similarities to the Doctor Who episode cannot be denied.

