Jigged bone is called that because it was jigged, or worked with a tool to create the grain. The bone typically used is cow's shin bone but it can be any other bones too. Newer jigged bone, done on computerized machinery, can actually have a much more attractive grain than old bone done by hand but it will not have that very attractive patina age produces. Stag is made from antler, an entirely different material from bone. Sambar antlers from Asia or Indonesia are the best, having beautiful grain and a small pith which is the soft "vein" in the center. European antler is also desireable and North American antler, from deer or elk brings up the rear.
It is easy to tell bone from stag. If you look closely, you can see tiny pores all over the bone. I've forgotten the scientific name for them but they are very easy to spot. Antler will have a nice tight surface with the pores in or around the pith line in the center, or end of the antler. Antler is a much more durable material but used for knife scales or gun grips, the differences between antler and bone are not really noticeable.
Bob
