I'm so glad it worked out for you. Sometimes all it takes is the threat of legal action, and things somehow just "work themselves out"
I'm happy to hear he came forward and fessed up-at least you know where it came from.
Now, I do have one question: Why was the vet putting a tattoo on a dog, when he didn't know what the tattoo WAS? He didn't know what the symbol meant, and why he was putting it permanently on a dog? That seems a little "off" if you ask me. Correct me if I'm wrong, but the only reason a dog would have a tattoo is for identification, right? Or are there people that give tattoos like people get tattoos? If that's the case, then what reputable vet would do that do a dog? ugh.
As far as the money goes, I think I'd take the neuter money and first get a few new things for Buttercup-some outfits, treats, leash, and his first visit to his new vet, and then I'd go out to dinner somewhere nice with my husband for a job well done! Think of it as your "reward" money for figuring out that mystery!