To mark, as sheep, by cropping or slitting the ear.
                  
                
                  
                    noun. 
                    A mark on the ear by which a sheep or other domestic animal is known.
                  
                
                  
                    noun. 
                    Figuratively, in law, any mark for identification, as a privy mark made on a coin.
                  
                
                  
                    noun. 
                    Any characteristic or distinguishing mark, natural or other, by which the ownership or relation of something is known.