The better makers of leg-of-mutton gun cases from H.H. Heiser down to
RED HEAD --
would have their logo prominently displayed on their cases. Leg-of-mutton cases made for Abercrombie & Fitch Co. would have their logo stamped on them --
My best guess would be, that whoever made your case, the 16G is the model number, the 28 means it is made for 28-inch barrels and the 1 that it is a case for one set of barrels.