DD-universal symbol
What you have to understand is that the Deaddrops project is not a commercial project, but an open one, of general interest, meaning that everybody can handle its execution and exploitation. I.E., ~97% of the DD database has not been completed by…

Solution

� the creator of the project.
Put in another words : Aram Bartholl did not create Manchester United, but he created football. You see ?
The project is universal, free, not bound by coercitive legal litterature or special licensing, thus the symbol must follow : extreme simplicity, basic and "safe" sources (a circle, two letters, Arial bold based), graphic neutrality. 
This project is totally in the same field of Copyleft and Creative Commons licensing.
The contest can stop here. ;-)

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I couldn't add a new design, so i edited the previous letter-based design ("Dd")

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