I use buck's initial, doe's initial, month, year, kit number. So CF815 would be from Captain x Feather, 8th month, 2011, 5th kit marked in that litter.
I use 0 for October, X for November, Z for December.
This way, if I lose all written and computerized records, or I have rabbits that resemble one another, I will always be able to check the ear tattoo and know who the sire and dam were and the month and year of birth. I am careful to have only one doe and one buck that have names starting with the same letter in my herd at one time.
If you have a very large rabbitry (more than 26 does and bucks), you could use lower case letters to bring it up to 52... but larger than that you would need to add characters or reverse the order so the buck and doe initials come after the numerals instead of before them.