cloven hoof

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A divided or cleft hoof, as in deer or cattle.
• noun Evil or Satan, often depicted as a figure with cleft hooves.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A divided hoof, as on bovine animals.
• noun The mark of the Devil.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the mark of Satan
• noun a hoof divided into two parts at its distal extremity (as of ruminants or swine)