On the subject of dogs and signs, when I was doing a course on civil law, we were advised that, in the event that your dog bites someone, in your defence you could plead that you had no way of knowing that your dog was dangerous. If however, you have a "beware of the dog" sign on your gate, this is regarded as an acknowledgment, that you know it is dangerous. Since you know it is dangerous, you have a duty to ensure that it cannot bite anybody. Since it has now bitten someone, you will almost undoubtedly be found negligent.
If you have a dog, you are therefore advised, NOT to display a "beware of the dog" sign. In the event that it comes to court you can claim that you didn't believe it to be dangerous, (therefore you are not negligent).