Snap! There goes the loud popping sound, somewhere in the vicinity of your ankle bones. Are you now faced with a broken ankle, or is it just a sprain or other injury? There are different symptoms that can point to a fractured ankle, although receiving qualified medical assistance from a professional worker is still advised, whether you eventually think it is broken or not (and even if you are correct, the severity of the injury may be something you can not tell, or it may need treatment that you do not know about or are unable to perform properly).
One of the symptoms of a broken ankle is a deformity in the area. Whether it's directly on the ankle, or nearby, it may point to a fracture. Of course, it could be a bone out of place, a partial dislocation of sorts (technically called a "subluxation"). If the deformity includes a sharp fragment or edge of a bone protruding out through the skin then you can even physically see the broken bone.
Pain does not necessarily mean that the ankle is broken, as it can accompany other conditions that may exist in the area. For instance, a sprain may have pain involved, perhaps even in a severe way in some circumstances. Also, a popping or snapping sound does not always mean a bone is broken, as sprains can also make this audible noise.
If the area is sensitive or tender to the touch, or when pressure is applied, it is possible that there could be a broken ankle bone. Also, if weight can not be put on the leg that has been affected by the injury, a fracture is a possibility. Again, these symptoms do not necessarily mean that the bone has been fractured, as you could feel tenderness or be (or seem) unable to place weight on the leg despite a different issue being the problem.