Did They Know Each Other?
William was more than shocked that this random police officer would know something like that when the two had never even met before. Had they known each other in the past or something? Maybe they did and William simply forgot?
His Bumper Sticker
Then it clicked: William realized the reason the officer knew about his service. He had forgotten about the bumper sticker he had on the back of his pickup truck. Anyone who saw it would immediately know that he had previously served in the army.