Crusader is right... your find is a brass ornament made to be used on leather. The spike on its back is "smoothly curled over" to keep it attached to a sheet of leather, such a saddlebag, or a carriage-curtain, or horse-harness. A furniture tack has a straight, nail-like spike, because it is driven into wood, with no need to curl the spike over "from behind" to keep the tack in place. Colonial-era shoulder belt plates often had several curled-over spikes on the back of the plate's corners, for permanent attachment to the leather shoulder-belt or cross-belt.