tattoos are used, like microchips, to identify dogs. Our local Golden Retriever rescue group tattoos all of it's rescue dogs so that they can be readily identified if they are ever lost. Probably the shelter you got Simba from, KayAnn, did the same thing. It is not uncommon. In our case, with all the hair a Golden Retriever has, I think microchipping is probably a safer bet. But for a short haired dog like Simba, tattoos should be fine.

Logan