Mongolians historically have kept dogs as working animals, mainly as guard dogs. This is changing in the city, but the traditional Mongolian dog retains its reputation for fierceness. Most Mongolians I know, if not afraid of stray and loose dogs are at least wary of them, with good reason. (Most stray dogs I've met, however, either avoid you, or are just looking for some love and attention.)
Signs like these, on the gate to a fenced-in ger are not uncommon. (Both the fence and the yard are called a hashaa in Mongolian.) This particular one is somewhere in the ger district surrounding Gandan (the main monastery) in Ulaanbaatar.