I love to use children's chalk or a soap stone pencils to make markings on my stones when I'm working. When I have to trim a stone or make a note as to the placement of my tie stones...ect.. In this case I used them a great deal when placing my stones steps. Making markings so I knew how far back to place them into my wall before lifting them into place with my skid loader. They also clean up well after the first few rain storms.
The children's chalk I just picked up at Walmart in the kids section. A full box of colors I figured would help go a long way. I also bought a Soap Stone Pencil from Ace hardware. The nice thing about the soap stone is that you can make more precise markings.
Plus who doesn't like to play with chalk? In this case I left notes for my client to try the steps. Of course they can't walk to far. But they can go up and come back down.
Tick tack toe any one?