My mom called them spit pens too, for the same reason. How weird.
I only mark as I go. I marked a whole one out once and the marks were gone by the time I got it all the way in my floor frame. NO WAY JOSE am I repeating that. I mark as much as I can work in once sitting at a time.
I either use spit pens and wash it out as I move it or I use plain chalk. It depends on the color of the fabric.