Radial nerve damage is identified by:

Radial nerve damage is characterized by a specific clinical sign known as wrist drop, which refers to the inability to extend the wrist and fingers. This is due to the radial nerve's role in innervating the muscles responsible for extension in the forearm and hand. When the radial nerve is impaired, a patient will struggle to extend their fingers, resulting in a characteristic presentation that can be observed during a physical examination.

The other options presented do not relate to the functionality of the radial nerve. Injury to the heel bone pertains to the lower extremity and has no connection to radial nerve function. Similarly, injury to the outer ankle bone is also related to the lower limb and would not impact finger extension. Lastly, mechanical blockage of the brachial artery involves vascular occlusion and does not directly influence the neurological function of the radial nerve. Therefore, the inability to extend fingers accurately reflects the consequence of radial nerve damage.