curl -i -X PUT "https://api.box.com/2.0/files/12345/watermark" \
     -H "authorization: Bearer <ACCESS_TOKEN>" \
     -H "content-type: application/json" \
     -d '{
       "watermark": {
         "imprint": "default"
       }
     }'

{
  "watermark": {
    "created_at": "2012-12-12T10:53:43-08:00",
    "modified_at": "2012-12-12T10:53:43-08:00"
  }
}