What about the Mothercrystal? (Symbolizing Hydaelyn naturally). If the actual graphic of the Mothercrystal is too detailed, there is the 'Mark of the Twelve'/Legacy Mark tattoo that is strongly hinted to represent the Mothercrystal (I found a graphic of it online without too much trouble, but being a third party site I won't link it here).

Another alternative is Azem's solar symbol on the Azem crystal, which.. is kind of appropriate (but I think Hydaelyn would be a more fitting symbol in the centre.).

Either way, that is a wonderful project Vidu!