On Hipstamp, though no longer on sale (
https://www.hipstamp.com/listing/al...0/56884490).If correctly described, then this is a Taiwan 1951 revenue duty stamp.
(The building in the stamp seems to be the Presidential Office Building in Taipei. It became the Presidential Office in 1950 after the government of the Republic of China lost control of mainland China and relocated the nation's capital to Taipei at the end of the Chinese Civil War.)
