An incredibly well-preserved seal.
The second image [above] is the sealing made from this seal, as shown in Shah, S. G. M. and A. Parpola, Corpus of Indus Seals and Inscriptions. 2. Collections in Pakistan (p. 16). On unicorn seals in general, the authors write (p. XXX):
"The unicorn' motif is placed first [in their Corpus] because it is the most common one of the Indus seals. The style of representing this animal in profile, so that just one single horn is shown, has in all probability been borrowed from the art of the ancient Near East. Although this representation undoubtedly has had a mythological explanation and importance in the Harappan religion the 'unicorn' is likely to be a real animal (likely the uris or Bos primigenius) which actually had two horns. It is in fact sometimes depicted as having two horns, but for the sake of analysis and classification these two-homed representations have been separated from the unicorns' under the immediately following heading of 'urus'."