XNEM (x-nem) is a wonderful source for marketing now. Imagine all the goodness that could spring out of this.
I like it too

But are 4 letter codes allowed?
Unfortunately, four letter codes has never been used. But they may have to open it up one day, when there are too many Xs around. ;-)
I'm pretty sure everyone will read xnm as x-nem, can't tell the same about xem (which sounds like some laxatives if I have to be honest)