Should I have the good fortune to end up with an Xmarks tartan kilt, I would be proud to explain to any passerby the nature of 'my' clan...and that they too can be sworn in if they have access to a computer, and have all the attributes required of friendly brotherhood. I think it's all refreshingly 21st century, and mixes well the flavour of clan-like support with the anxious times we now live in.
I also think the suggestion of a dandelion emblem should be applauded. To me this plant has several apt qualities:

Its roots can grow very deep, and are not easily removed.
The seed head is almost perfectly round like our world, and help in its future survival and distribution requires just a mouthful of breath to 'spread the word'.
It establishes itself almost everywhere, and if, in times when we're down, we happen across one it reminds us that there is ready support waiting to make things easier - even if only through helpful words or advice.
The bright yellow of the flower is the most cheering colour of the spectrum, but, as a lovable rogue, can have its mischievous ways as well.

If that doesn't sum up the Xmarks 'rabble', then nothing will.