Eagle-eye television viewers in mainland China noticed a strange discoloration on the suit lapel of President Ma Ying-jeou of Taiwan during a news report on Friday. The network was showing images from a news conference that Mr. Ma held in Taipei to talk about his historic meeting planned for Saturday in Singapore with President Xi Jinping of China.

Television viewers in Taiwan watching the same news conference knew why a tiny patch of Mr. Ma’s dark suit had been covered with a gray computer graphic: China Central Television, the state-run network in mainland China, was trying to mask a pin of the flag of Taiwan, or the Republic of China. The broadcast of the news conference on Taiwanese television was uncensored.

Twitter and YouTube postings by China Central Television showing Mr. Ma standing at the podium also had the flag censored. (Both Twitter and YouTube are blocked in China.)

#HKFP State broadcaster CCTV blurs out Taiwan flag pin worn by Taiwanese President Ma Ying-jeou … https://t.co/cu2zwqB8qe — Hong Kong Stream (@hkstream) 6 Nov 15

Because China insists that Taiwan is not a separate nation, and most other countries agree with that or subscribe to a “one China” policy, public displays of the Taiwanese flag can be problematic — not just in China, but also in international venues. When Taiwan takes part in the Olympics, for example, it does so under the name “Chinese Taipei” and its athletes carry a special white flag designed for such occasions, rather than the flag of Taiwan, which has a red-and-blue field with a white sun projecting rays.

The Kuomintang, or Nationalist Party, first used that flag in 1917, when it was establishing rule on the Chinese mainland after the collapse of the Qing dynasty. The party then designated it the official flag of the Republic of China. The Kuomintang lost the civil war to the Communists in 1949 and retreated to Taiwan, where it is the governing party. Mr. Ma is a member of the Kuomintang, which will vie with its rival, the Democratic Progressive Party, for the island’s presidency in elections scheduled for January.

The leaders of the two factions that once contended for control of China have not met since Chiang Kai-shek and Mao Zedong spent time face to face in Chongqing in 1945. At the time, the administration of President Harry S. Truman of the United States was trying to broker a truce between the Communists and Kuomintang and to set up a coalition government in China after the defeat of the Japanese invaders.

Follow Edward Wong on Twitter @comradewong.