This is a ballpoint pen, a collaboration between Disney's Mickey Mouse and Mitsubishi Pencil (uni). It seems that if you sent a reply postcard, you would receive a name stamp featuring Mickey Mouse. However, since this product is from several decades ago, I assume the service itself is no longer available (I haven't checked). The product itself is a rare item, so how about adding it to your collection? It is a new, unused item, but the ink is from that time, so please replace it.