Last week an unnamed group (commentary elsewhere) ran this full page ad (below) in The Washington Post disagreeing with the use of Sea of Japan over East Sea for the body of water between the Korean peninsula and Japan. The series of ads has also appeared in the New York Times and Wall Street Journal. The group also has informational pamphlets on several other contested issues.
In the US English, the conventional, Federal Board of Geographic Names toponymn for this body of water is “Sea of Japan”, and the conventional alternative name is also “East Sea” (Tong-hae romanized from Korean native script). When space is available, the placename is shown as “Sea of Japan (East Sea)”. As with any placename, alternatives are dropped under space constraints (such as with a 1 column map).
When the 8th Edition National Geographic Atlas of the World was published earlier this decade, a similar campaign (though more threatening) was run about the Persian Gulf (Arabian Gulf).