〒 is the service mark of Japan Post, the postal operator in Japan. It is also used as a Japanese postal code mark. The mark is a stylized katakana syllable te , from the word teishin (communications). The mark dates from the pre-World War II era, when literacy was less complete, the katakana symbol being more easily recognized than a kanji. (https://en.wikipedia.org/wiki/Japanese_postal_mark)