Hollywood

License Plate
Halfred Glitchbot's trailer on the last point of Hollywood has a licence plate.

It reads CALIFORNIA 88GNAKD.

Odds are it's a reference to 1988's comedy The Naked Gun : From the Files of Police Squad.The plot : an international terrorist group wants to humiliate the United States and plans on assassinating the Queen of England in visit in Los Angeles during a baseball game she will attend. They plan on using a device that can control the mind of anyone in a crowd and force them to want to kill an assigned target. They use it on a baseball player who will manage to get close to the Queen, fortunately clueless police detective Frank Drebin will prevent that.

The background story of the Hollywood map in Overwatch is that the attackers are Halfred Glitchbot's bodyguards, they have to escort him safely to his trailer on the movie set of his latest production. Being an omnic film director, Glitchbot is facing severe opposition from anti-omnic groups and apparently the situation is preoccupying enough that he needs bodyguards escorting him, even within the studio's property.

Unused Billboard Signs found in the Game Files
This is a texture file found in the game files of Hollywood.-AXIOM

-SIGMA COUTURE

-XOXO

-MZUZU cosmetics ("cosmetics" is really small and hard to see, it's at the bottom)

-petdiet industries

-melville homes

We've seen the first two companies of that list in Numbani and in the comics Going Legit as well as Sigma in Reflections.

The other four aren't found anywhere else in game nor in comics, animated shorts or origin videos.

Despite being in the game files, they aren't used in game. It's quite common for texture maps to be in the files even though only a small portion of the textures are used in game while most of the map goes unused in the end. Still, it means that at some point during development, the Overwatch theme designed those, surely they meant something back then and they may appear in game in the future.