Jonggi(宗旗) is the symbolic icon of Tiantai Buddhism that yellow vajra (金剛杵) is erected
vertically on three blue circles piled up. Making the both ends in the middle of vajra a
branch is called Dokgo (獨鈷). Making them three branches is done Samgo(三鈷). And making
them five branches is done Ogo(五鈷).
In India, vajra was used as weapons. In Buddhism, Vajrapani (金剛力士) that defends Buddhism has vajra because it symbolizes aspiration for Buddhahood (菩提心) which renounces worldly desires.
Yellow vajra that represents the center, the middle, symbolizes that Buddha's wisdom is midway (中道).
The shape that vajra is erected means the spirit of attaining Buddhahood (上求菩提) and saving the (distressed) masses (下化衆生) of Mahayana Bodhisattva who seeks enlightenment in the upper part and saves the people in the lower part.
Blue that represents the east means infinite prosper and at the same time, Korea located in the East.
Three blue circles mean three types of the truth of empty (空), false (假), and middle (中). The three circles piled up means that three types of the truth are combined with one another. All the things in the universe include empty (空), false (假), and middle (中). Three types of the truth do not separately (獨立) exist but are combined with one another. Accommodation of threefold truth in harmony (三諦圓融) means that there is one type of the truth in the middle and the rest of the truth are all equipped.
And three view points in a single thought(一心三觀) means to make this reason one.
This is samatha-vipasyana, the key asceticism method of Tiantai Buddhism. You have to realize that all the things in the universe[諸法] are the real state(實相) and midway(中道) through samatha-vipasyana. And you have to get the point that you can find Buddha's enlightenment as preached in the Sutra of the Lotus through asceticism.
The truth of midway (中道) is to get rid of two extreme viewpoints of 'all the things in the universe are empty(空)' or 'all the things in the universe are false.' If you do not stay at any place and get rid of obsession, this is the content that Buddha realized.'