If in the USA and flying as a hobbyist, pay the five dollars and display your numbers on the aircraft.
Make sure you go to the official FAA site and not some advertised site that wants to charge more for a sticker package. A Sharpie pen will work just fine if you don't have a label maker.
This is just the beginning of your new journey. Study the areas pertaining to recreational fliers. Then continue on and study the Part 107 areas. Nothing says you must get your Part 107 Certificate, but the knowledge of what it entails is priceless! Use this forum as your Q&A arena.