Have keys for multiple addresses? Generate a key fob with each address's house number on it. Have old cars? Label their keys with the model year. Apartment or hotel room keys? Label them! ...or pretty much anything else where you want to label keys with a number which goes higher than the 0-99 range my round keychain fob (https://www.youmagine.com/designs/keychain-number-fob-round-0-99) can accommodate.