Upon entering a little country store, the stranger noticed a sign saying "DANGER!  BEWARE OF DOG!" posted on the door glass.

Inside, he noticed a harmless old hound dog asleep on the floor near the cash register.

He asked the store's owner "Is that the dog folks are supposed to beware of?"

"Yep," the proprietor answered, "That's him."

The stranger couldn't help being amused.  "That certainly doesn't look like a dangerous dog to me," he chuckled.  "Why in the world did you decide to post that sign?"

"Because," the owner replied, "before I posted that sign, people kept tripping over him."