Yeah- I use vermiculite for the most part. It has gotten harder to find just straight up vermiculite-most of it is the Miracle Grow brand that is loaded with fertilizers, plant food and such. I finally found some plain old vermiculite at a different Lowe's than my local one. Just thought I'd give the peat a try based on that article I read. Yes, I mark the tops with a Crayola brand marker. They are washable and non-toxic, so I've never had any issues I could associate with it. I wouldn't want to use something harsh like a Sharpie.
Have you guys ever tried hatch rite? That's what I'm currently using.