Like the new little cap-top swatches on the redesigned NerdLacquer bottles? DIY that shiz on all your other polishes! Kits come with ten round white .5" super-strong adhesive labels, and ten round dome-top clear epoxy seals. Just paint your stickers with two coats of polish, let dry COMPLETELY, peel off and stick 'em on your bottle caps, then top with an epoxy dome and press down firmly. Voila! Now you can tell at a glance which color you're looking at even if your polishes are stored in boxes or drawers!
NOTES : These will work on any polish cap that has a flat top of at least half an inch in diameter. To aid in sticker adhesion, you might want to wipe off the caps with rubbing alcohol to remove any skin oils etc. Do you HAVE to use the stickers? Well...kinda, yeah. Polish does not adhere well to the slick plastic surface of most caps, and even if it did (or if you abraded it or otherwise jacked up the slick surface to aid adhesion), it's still a lot easier and neater to paint the stickers, which have the same diameter as the epoxy seals. Plus, your colors wouldn't show up nearly as well if you painted them directly on a non-white cap.
Will they fall off? Assuming normal handling and use and proper application, nah. Yes, you can peel/pry them off if you like, but they shouldn't ever just tumble off on their own!