Angle-kin Society
Group
The only reference we could find to this society was on the website of the National Churchill Museum which has some documents in its 'Environics Collection' which is about how St Mary the Virgin Aldermanbury was moved to Fulton, Missouri. So we guess the society is (was, probably) an American-British Friendship group set up after WW2 and that the Charing Cross plaque was erected then.
See other memorials in this area