I think the only type of security sign that can actually be helpful is an alarm company sign. Announcing you have guns just encourages bad guys to be extra sure that no one's home when he comes to take your guns away from you.
"It is long been a principle of ours that one is no more armed because he has possession of a firearm than he is a musician because he owns a piano. There is no point in having a gun if you are not capable of using it skillfully." -- Jeff Cooper