The story
From wand (“handheld narrow rod, used for instructing or pointing, or as a traditional emblem of authority”) + of + peace.
Etymology from Wiktionary, CC BY-SA 4.0.
wand of peace
Today it means: A wand or staff with a silver tip which was given to an outlaw as a sign that they were restored to the king's or queen's peace; and also carried by a messenger of the monarch as a symbol of office, to be broken in protest in cases of deforcement (“resistance to the execution of the law”). Full definition →