Look carefully at Jaejoong’s hand. Notice the black mark, right? Now look at the picture below.
Fans captured a picture of Jaejoong’s hand and found out that the black mark looks like Yunho’s name in Korean - 윤호
This can look very confusing to fans who can’t read Korean, so I’ll try to describe it.
First, on the left character, at the top, there’s a round dot or circle that represents ‘ㅇ’ and underneath is ‘ㅠ’. The last mark on the left character is not to exact to be sure to point it out as ‘ㄴ’ even so, if looked at the character as a whole, it’s easy to figure out that it says ‘윤’. But the ‘유’ part seems to be pretty correct.
Now, on the right character, at the top, there’s a line that’s vertical meeting with a line that’s horizontal and below is a round dot. This portray ‘ㅎ’. The very top line of ㅎ is commonly written in a style of the top line being vertical to Korean people. And Jaejoong is also one of them. Look at the picture below which a photo of Jaejoong’s signature to 윤재블랙홀 (YunJae Blackhole). Jaejoong wrote the last character ‘홀’ with the top line being vertical.
Okay now moving on, under is ‘ㅗ’. It doesn’t look straight nor rigid, but in my opinion, I think he has written ‘호’ connecting it. As a Korean, alot of Koreans when writing hangeul, they don’t try to write it perfectly one by one. We write simple and fast. If I compare it to English, it’s like writing cursive.
Beside saying that’s 윤호, some people say it could be Japanese since at that time, TVXQ was performing in Japan and the right character looks like ち (chi), but then again, the left character doesn’t look similar to any other japanese characters.