A rabbit just like you has a left and a right side. So if you are facing your rabbit its left ear would be on your right. This is probably the ear with the tattoo unless whoever done the tattooing tattooed the wrong ear. This is used to identify the rabbit (kind of like a name); all of our rabbits have both a name and a tattoo.
This number can be anything the breeder wishes it to be all numbers, letter or a combination of letters and numbers. It can be a single number or letter or as many as can be squeezed into the ear (so a long eared lopped rabbit could have a much longer tattoo than say a short eared Netherlands Dwarf). Usually they are between 1 and 6 characters in length. This is just away for the breeder to be able to go back and look at their records and be able to identify a rabbit and any information about it, birth date, parents, siblings, and such. Depending on the records that breeder keeps.
To show; most show rules and all ARBA sanctioned shows state the rabbit must have a legible tattoo must be in the left ear.
According to the American Rabbit Breeder's Assoc (ARBA) the rabbitâs right is reserved for a resister mark or registration number. Your rabbit is probably not registered or it would have a tattoo in both ears. For a rabbit to be registered with the ARBA it must have a pedigree with a minimum of three generation listed (Mother, Father, 2 Grandmothers 2 Grandfathers, 4 Great Grandmothers, and 4 Great Grandfathers) and a tattoo identifying it in it's left ear.
Hope this helps. Most of all enjoy your rabbit.