On this day in 1919, The Black Sea port city of Batum had stamps issued for it which were then used during the occupation by British forces from December 1st, 1918 until July 7th, 1920. 

Batum 1919 blk 25-ruble on 5-kopeck claret Russia Coat of Arms, Scott 33.

An example of one of these stamps can be seen in this article (originally published as a column in The American Philatelist April 2019 issue ), which emphasizes the importance of getting such stamps authenticated as many forgeries exist. Bushire, Batum, Heligoland, and Samoa are just four of the 175 other stamp-issuing entities covered by our experts within the last year. stamps from Batum are also mentioned in the Index of Literature in the English Language that Describes Postal Stamp Forgeries, Fakes, Reprints, Fraudulent Postal Markings and Other Obliterations. and Bibliography by Theodore M. Tedesco. This index provides many resources to help collectors identify these forgeries. 

An example of a cover from a lot sold by Daniel F. Kelleher Auctions

Also on this day, American aviator Ruth Law carried postcards on a flight to the Philippines in conjunction with the Manila Exposition, beginning airmail service in the islands. The cards are inscribed "Aerial Post Card to Commemorate the First Aerial Mail Service in the Philippines, April 4 and 5, 1919". Cards dated April 5 were not flown, according to the American Air Mail Catalogue. You can learn more about the postal history of the Philippines in this article and learn more about the history of airmail between Madrid and Manila here.