I have a lot of balls for different purposes: Ball machine, my wire hopper and 6 newest balls. I've been using an oversized permanent black sharpie. I write the date on the new balls but it usually gets blurry pretty fast. Once I tried a stencil and spray paint for my machine balls but it took ages. Fingernail polish, a stamp? I haven't tried these. On my older balls I'd just like to put a simple mark with a distinct, permanent color. Any tips on the latest, greatest way to do this are appreciated!