This sign really needs no translation. It says exactly as you might guess: Savage Dog, Beware! (Mouken Chui).
Playfully ironic, I'm guessing, as I was able to get close enough to snap this picture without any growls or other signs of doggy life.
In America, one takes Beware of Dog signs seriously. I've had enough run-ins with mean, nasty, aggressive dogs to make a wide berth whenever I see one straining on a leash.
Dogs here are different. There's a shiba-inu on the corner whom I pass practically every day. He stands with his front paws on the top of the cement wall and watches me quietly as I pass.
The most you hear out of dogs here is when the sirens for ambulances or police go off. Then they start howling in unison, responding to the call. This midnight howler lives across the way: