It is definitelty criminal vandalism. It isn't Grafitti, which is an artform and in which the artists either tag their work or use distinctive style. There is clearly no style and the person doesn't want to be known by their work.
But... I didn't know that JWs are only allowed to call and write to people they know. Most JWs aren't supposed to know non-JWs well enough to know their phone numbers and addresses. So, does that mean they are just calling on each other? If I were still in, I would probably call and write to every witness I knew every week and count the time since that is what they are being instructed to do. But you can't grow numbers by advertising to yourselves. Could COVID be how the organization goes down? If they are only witnessing to people they know, then they won't grow. If they are only witnessing to each other, then they will annoy the crap out of themselves. That would be hilarious if that was what it took to bring down the org.