Normally, the crown is only shown on products which are provided by suppliers to the Royals. Often worded as "Purveyors to the crown" or "...to the King (or Queen)". These suppliers secured a contract with the crown to produce their product, anything from cheese, to furniture, to pottery, and yes, even to buttons. These purveyors then earned the right to display the crown on all their products, which was a nice selling feature. Anything "Fit for the King" was usually good enough for anybody else. But it wouldn't necessarily indicate a military use. I gleaned this info from the series BBC programs, aired on PBS, detailing the history of Britain and narrated by Prince Andrew. Hope that helps.