The icon is a dog house logo with a hellhound face as shown in the image above You'll want to clear out all the nearby zombies before approaching the dog house. Then, interact with the dog house.

Call of Duty: Modern Warfare 3 Zombies has many Easter eggs, one of which allows you to pet a hellhound. You can also use its abilities to advance in the game, including using it to revive yourself.

To unlock the secret "You can pet the dog" achievement in MW3 Zombies you must pet a Hellhound. It is a secret achievement or trophy depending on your platform, meaning it's not a task you can ...