On closer inspection, they had a message for pup owners (or bad boyfriends?):
Don't know if you can see it very well, but that's a drawing of a dog with a cat on his head on the license plates. California has a special plate that was just announced last September, which helps raise funds for free and low-cost spay and neuter. (Might have to get me one of these next time my registration is due...)
The artwork was done by Pierce Brosnan. Who knew? It's based on his dog, Shilo, and their cat, Angel Baby. You can see the artwork on the license plate and read more about it here, and also see a picture of California's "first dog" - apparently our governor, Jerry Brown, has a corgi! Again - who knew?
Thanks to our neighbors for spreading a good message in a fun way!