A ‘beware of dog’ sign does not eliminate a dog owner’s duty to be safe and to keep the people who come into his or her property or their home safe.
A “beware of dog” sign is not a “get out of jail free” card. For example, if you have a “beware of dog” sign but you’re going to let the dog out the front door when the mail carrier rings the bell, that’s not enough.
If you’ve invited someone into your home and then the dog bites them, you’ve already implied that the home is a safe place to be, regardless of the signage.
Additionally, we would consider the act of posting a “beware of dog” sign as an admission that the dog owner knew that their dog was dangerous.