Here is a customizable Sharpie pen cap that is set up for AMS and can be customized by changing the letter shown at the top of the cap. There is a letter on each side and each is changed independently in the Objects panel. You can also print in one color with the customized letter.

To attach to your Sharpie, remove the pocket clip on the Sharpie cap with a pair of sharp cutters. Test fit the sword cap on the pen, if it slides off, add a drop of glue inside the sword cap, put it back on the Sharpie cap and you're good to go.