I use a sharpie as well, once I have the ammo in box I run red line through them. One line for 230 gr , a "X" for 200gr and so on just so I can quickly dbl check Im into the right box or right mags. After awhile others at the range I compete with quickly learned what my brass looked like as well.
Some use nail polish, some use other marking methods, another shooter uses a sharpie with a different color ect.