There are several Easter eggs in Overwatch tied to Murlocs. Coming from the World of Warcraft universe, Murlocs are a froglike-fish people that tend to live in swampy areas.
The biggest example is in Hanamura, just outside this ramen noodle restaurant. If you shoot this Murloc, it even makes that bubbly-voice sound these little guys are known for.
On the same level, you can find Murlocs in the arcade. The arcade has some drink vending machines with Murlock pictures on the bottom.
Have you ever tried to catch a Murloc? It's not easy- unless you have Murloc bait. This Easter egg is found in Ilios, in glass display case.
Finally, there's also Murloc graffiti found on the side of a vehicle in the Temple of Anubis.
Obviously someone at Blizzard really likes these little guys.