They're Corps of Military Police but I can't think of anything in their equipment which would fit in a small box like that. Maybe a knuckle duster to save them taking their belts off to sort out bar brawls ?:grinning:
I've been thinking along similar lines, what does a Military Policeman carry that other motorcyclists don't, a truncheon, notebook, white traffic controllers sleeves, handcuffs? and the missing box on one machine may suggest that it was removable?