The physical characteristics which will enable you to tell the difference between a grizzly bear and a black bear are the presence of a shoulder hump, the shape of the facial profile, the size and shape of the ears, and the length of the front claws.
Grizzly bears have well-developed shoulder muscles for digging and turning over rocks. These muscles appear as a prominent shoulder hump between the front shoulders, which is visible in profile. Black bears have no shoulder hump. A black bear's highest point, when it's on all fours, is the middle of the back or the rear, depending on how the bear is standing.
Grizzly Bear - Shoulder hump
Black Bear - No shoulder hump