I'm writing rules for a board game. It's similar to dots and boxes, and I would like to have a nice general word or phrase to refer to what the players use to mark their moves on the board or paper, since one could conceivably use anything to do it, like a pen, pencil, crayon or even a paint brush if they wanted to use one.

The best I could think of was drawing implement, but that sounds too technical, and I'm trying to shoot for the lowest reading level I can. 

I also thought about drawing tool, marking tool or maybe even just marker? What do you think?