By "fur trade" I take it you meant mountain man- not the buck skinners or long hunters "from Kentucky". There are two choices, cow and buffalo. On the cow horn you can probably just copy any style of the day (staple or wood finial on the base plug). Alfred Jacob Miller, who painted the mountain men usually depicted some sort of finial but I can't tell if it is wood or brass. The museum of the fur trade has a buffalo horn with a staple in the base plug. I would say on the buffalo horns you want to keep them fairly plain, not all sorts of carving, etc, in fact the same would also hold for a cow horn used in the west, plain is probably more pc.
If you want, you could also put another staple in the throat area, if the horn there is too thin to carve any rings, etc.