Usually, when you buy a registered horse, usually, the seller will give you transfer papers with their information on them as the seller/previous owner and then you just have to fill out your side, the buyer/new owner. Of course, as you mentioned, you have to join APHA and pay to transfer the papers to your name. If you didn't receive transfer papers, you can either contact the person you bought your horse from or APHA to help you figure out what to do. I had called APHA for help because I had bought Sierra through an agent and I didn't get to meet her previous owner (long story). They are very helpful though. Might be best, though, if you do know the seller and can work with him/her on that. As for tattoos, my 1st horse was also a TB, so I know what you're saying about tattoos. APHA does not tattoo as a practice the way Jockey Club does. Any identification marks you wanted to do (tattoo, hot or cold branding, etc.) would just be your decision, not something required or regulated by APHA.