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I'm really liking the 2nd design but the idea (that someone else mentioned) of the little 'b' & 'd' pattern sounds cool.
Also, as you've given it a proper 3d perspective, could you actually complete both letters, as the bottom back of both the letters is currently missing.

I think the missing back of both the letters adds to the design. Now it's up to me to make it clear it's a 'b' and a 'd' with the missing back ends.