The registration is for YOU, not the bird. The registration is in essence a license to operate. It says that you have read the rules, understand the limits for flying etc. If you buy 20 drones, all of them under 55 lbs (I think), you do not need to register more than once. Think of your registration as a driver's license. Edit: Apparently some users had to provide the Serial Number(s) of their drones. I do not recall this when I did my registration.
Now, there are some 'plusses' to having a sticker attached to your drone:
1. You're complying with the law
2. If your bird gets lost and someone finds it, they can trace you back based on the registration number. Here, I added my phone number and email next to the registration number.
3. Most importantly: If your drone crashes and breaks someone's window or causes a traffic accident, they will be able to find who the culprit is (You). Now, some might see this as a negative but I do see it as a positive: If I'm traceable, it's an incentive for me to fly responsibly.
So, in summary (1-4 are a must):
1. You must register on the FAA site (read the document that came with your drone, or download it from the DJI webpage)
2. Print Your FAA registration number and affix it to your drone (outside, or inside, near the battery)
3. Also include your email and phone number in case you lose the drone
4. Read the manual that came with your drone, and whatever you can download for DJI
5. Put a TXT file on the micro-SD card, that includes your registration ad contact information as well, again, just in case you lose the drone and need to recover those precious memories on the SD card.
6. If you're really 'scared' of losing your drone (especially if it's an expensive one), buy and attach a GPS tracker to it. Very optional, of course.
I hope this is helpful. What else do we need to clarify/discuss/debate?