It's a creeper seal. It might not be apparent in the rendering, but there's a creeper face on the square part. (On the bottom in the rendering) In the time when people actually used letters, they would put wax to seal the envelope, and then imprint the wax with their seal. If you imprint wax with this seal, you'll see a creeper face!To use, just pour wax on the envelope and stamp with this seal!