VOID residue from yellow sticker on screen door
Olive oil or 99% isopropyl rubbing alcohol; depends on what type of glue. You'll be able to tell which one is working or not.
We took a picture of ours and filed it in a digital album with other related pics (vehicle plates, etc.) and left the stickers on the trailer.
2015 Jayco X213
2014 Ford F-150 Platinum EcoBoost w/ MaxTow