Conventions are meant to foster the free exchange of ideas. Greg, one of the guys in our gaming group, saw at Fall In 2016 that the folks in Canada who play a lot of This is Not a Test made nice game markers. He told me about it, and when I returned from the convention, I ordered the bottle cap covers and hole punch from Amazon.
Apparently girls are making jewelry from bottle caps. I understand that people even sell bottle caps that were never on a bottle but have pretty designs. To protect the paint on the top of the bottle cap, someone started producing these self-adhesive, clear, slightly bevelled bottle cap covers. They are made form a very soft rubber and come in sheets.
I made some markers in Power Point and printed them on card stock. Then I used a one-inch hole punch to cut them out nicely. I peeled the clear bottle caps from the plastic sheet and stuck them to the markers. The result looks pretty nice. Be careful when remove the covers from the plastic; if you touch the sticky side, you will leave finger prints.