Yes, it's a pet identifier. The chip is small -- about the size of a large grain of rice, but I can still feel them embedded between the girls' shoulder blades. In case they are lost and sent to a shelter, they will get scanned, traced to me, and returned.
My vet scans them on each visit and the microchips are still working.
[How about that -- a pre-war application of the word "embedded"?]