The Real Doctor and I spent a chunk of yesterday giving some of our newer animals unique identifiers. The lambs got their ears pierced for a fashionable plastic earring; it carries info about our farm and a name and number specific to the sheep. The marks of these beasts are duly noted by the feds, who have an interest in keeping track of scrapie and such diseases.
The tool of the day, though, is the Ketchum Revolving Head Ear Tattoo Pliers. (Pictures from the Nasco catalog, for all your farm and ranch needs.)
The holes in the jaws of the pliers hold individual letters. For example, this is the letter "A", upside down.
The revolving head is nice, because you can load up the tattoo for the left and right ears at the same time. While the poor, innocent little goat is restrained, you can smear the ears with green ink (which gets all over the place; annoyingly, the little tube is packaged under pressure so that when you open it, five mls of gooey green blorts out over everything), and wham! wham! before the poor, innocent little goat knows what hit her, she's got the baddest tattoos this side of Mike Tyson: