Now I’m scared
It’s not uncommon to see these kind of signs in backyards around the country; even people who don’t have a pet sometimes put these up as a means to ward off burglars, and more often than not, it works – no one wants to take the chances. However, the sign isn’t as effective when the dog is behind it, rolling on grass.
Some people adopt dogs hoping they would function as guard dogs, but that’s not always their nature. Usually, even dogs that seem big and intimidating are kind and friendly, much like this one! It doesn’t seem like there’s any danger here, and if anything, the only danger would be this dog is so cute, you wouldn’t be able to stop petting him.