We already have a three letter currency code for Ether - ETH (http://forum.ethereum.org/discussion/433/ether-currency-code-poll-eth-vs-etr-vs-other
), but did you know the symbol for Ether?
Ξ has the interesting properties of:
1) having already been in use for a while
2) looking fairly elegant
3) can be stylized easily but more importantly...
4) it comes from the community!
I had to do a little digging in my archive and found that nucleo_io on reddit (@Manfred_Karrer
in this forum) was the first to reference it on the 13th of January 2014.
Here's the thread for the historians amongst you: http://www.reddit.com/r/ethereum/comments/1v5tjm/ether_symbol/
PS: oh and errr... Ξthereum <- looks cool