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My first reaction to this was it looked kind of like some science equation. Since I'm a designer and not a scientist, I'm not sure if the combination of ef represents anything in that field, but it might be the combiniation of the fonts. Maybe I'm seeing f for Farenheight and the beginning of E=MC2 Then the bar looking like a diving line doesn't help with the equation theme.
I like the idea, I just think there needs to be a little more clarification.

PS- #6 is my fav.