Last I was in touch with Marshalls was ten years ago re a guarantee and replacement for a ferret that had to have teeth pulled....canines very much maloccluded and causing damage....ANYWAY. Used to be one dot meant first shot, second dot meant fixed. Other ferret farms tattoo also, but different systems.
Also, some rabbit shows won't let you show without a tat. And, as a side note I have known experienced rabbit people (in it for 20 and 30 yrs) that lost bunnies while tattooing them as they threw a fit and broke their own backs or simply damaged nerves and never moved right again.