I've become quite taken with the significance a marking can hold. I think in terms of a permanent one I'd echo being very careful about what you do and don't do anything that you're not completely sure you can live with keeping.

I'm cosidering a tattoo quite carefully these days, one that specifically speaks to me and my woman. I've never got one before though. And I don't plan to run out and get one any time soon, but it is something I am looking at for down the road. I wouldn't be scared about doing it, because I'd never allow a permanent marking of myself unless I was 100% sure about having that with me forever.

In a sadomasochistic sense, I have marked myself with a knife, but not permanently. I was careful to choose a spot I knew would be covered by my day to day clothing all the time as I have no desire to explain why it's there. I quite like "temporary markings" that one can get with all sorts of BDSM acticvity. And the best part is when you go away you can always make more.