I've used stickers...esp. for which card is synced on Amex to which social media site, ect, 2x gas, grocery, office supply, automotive, ect. The stickers can be an issue with card swipers so positioning away from the top of the card is better. I started using a black marker lately.
Used to be the MillionMileSecrets had a site to enter your cards on (not the actual numbers) and it would tell you which card was better to use for which purpose. It was too complicated and cumbersome to keep up and he quit it.
Welcome to FlyerTalk!