ear tag

Short definition from Wiktionary

Noun

1. 1
   A tag attached to the ear of an animal (usually a farm animal) to identify ownership.
2. 2
   A benign growth of skin or cartilage on the ear near the tragus.

Verb

1. 1
   To apply an ear tag to an animal.
2. 2
   to attach an ear tag to the ear of an animal.