^Oh... I'm not sure... I think Yoochun has been using the "keep the faith" for a long time, before all this. When fans knew about the issue between SM Ent and TVXQ we started to use it becase we should keep the faith always, and always trust them no matter what.
I think the "keep the faith" thing got bigger thanks to an international project made by fans. A webpage had the idea to make support videos; in those, fans had to write a little message to TVXQ with the text "always keep the faith" too. It was a total success and even korean media reported about the international project.
That's only the first part. There are many parts of the project and other fanclubs started to do the same, it got REALLY big. This is the complete playlist:
http://www.youtube.com/view_play_lis...B530013F7C2A35
I think TVXQ also saw it, because a few days later we could see a new tattoo in Yoochun's chest which said "always keep the faith" AND Jaejoong has one on his chest too. These are the pics:
Media has been saying many things about the issue, most of the time rumors and false stuff which has created confusion among the fans. That's why we only trust what Junsu, Jae and Yoochun & their representatives say.
So... This is the explanation. I'm not completely sure about the origin, but I know how it has gotten bigger and it's now our motto.
Now you can use it too

ALWAYS KEEP THE FAITH GUYS!