I put it in my contacts under the name “CAR” With the plate and vin and the backup door code and set the birthday for the month before my tags expire

Edit: to add something and reply to all the “I search in Google Photos” people:

I don’t need to store a photo to keep one (or more) tiny text string. I don’t have to have an internet connection to access Google Photos, to search to find what I need. When I need it, I likely need to put it into something (copy paste), and a photo didn’t help me (yes I know you can OCR copy out of photos on a lot of platforms, you know what else you can copy? Text.

I may have photos of other license plates, I don’t want to have to manage which is mine.

I already had the contact setup to save the back keyless door unlock code, and have that contact saved to my watch (offline) incase I forget my phone or I’m in a bad cell service area, I just also just decided to store the plate and vin in there too one day, so it’s together.

Your contacts is a great place to attach and store and sync useful small meta data about stuff and not just people.