What is the significance of the double Yud used as a stand-in for G-d's name?
When you have two Yudin (or in Polish Jewish pronunciation, "Yidin" - also means "Jews") who get together on an equal level, neither of them putting themselves higher than the other, then you have Hashem's presence there. (The "Holy Jew" of Pshischa, cited in R' S.Y. Zevin's Sippurei Chassidim to Num. 14:20)