I think they're rotating through different neighborhoods offering free rabies shots. About a month ago my lady told me it was available in our neighborhood. As my three adopted dogs aren't allowed to roam the soi freely, they're at a very low, low risk for rabies so declined to give them the shot.
Edited to add: It's also great they're offering free sterilization. I paid for the procedure when I took each of my three previously soi dogs in.