MrFreeze
To be fair, the Society does tell JW's to use discretion when you see "Beware of Dog" signs.
My understanding is that this wasn't a case of not them not heeding signs. They knocked on some guy's door and the dog came surging past the owner and attacked them. It's a perfect example of how you just can't predict what will happen when someone opens their front door, or say with certainty that the outcome will always be harmless.
Speaking for myself, I was once attacked by a dog in the preaching work before even crossing over onto the person's property. The gates at the end of the driveway were shut and I was trying to get the owner's attention on the buzzer. The dog managed to leap over the fence and attacked me on the sidewalk. The point is, there is always an element of risk to the door-to-door work, signs or not.
Cedars