I'm a handyman and accidentally found "tile spacers". They come in all sizes and some great shapes and I use them to identify units that have fired and such in many games. They are cheap and you get a bunch in the smallest of packs. I use the smaller thin "X"s and put them on stacs to note fired, and I'm sure you could find another shape or color to note turned.
https://i.ebayimg.com/images/g/4vUAAOSwnDxUq4fP/s-l300.jpg