Personalized Engraved Pet ID Tag, available at Petco for $11.24
At the very least, your puppy should have identification tags attached to their collar or harness when they're outside in case they get loose or lost. List all important information like their name and your contact information on it so someone can actually find you and return your pup.
If you want to get fancy, places like Petco can even engrave your tag if you stop by the store.