The photo of the bus looks to looks like one of those (motor home sized) rental car shuttle busses they use at the airport and it appears to be heading to a construction site. I'd say this is a society owned vehicle and it is transporting workers to an Assembly Hall build or something similar.
To me these buttons are similar to wearing the assembly lapel badges to restaurants etc during the assembly. They give the wearer the feeling that they are making a difference somehow but usually no one notices.
Either way, I've really noticed lately that individual JW's are always on the look out for proof that they are a legit religion. They don't seem to be all that sure and think if they say it enough times, it will be so.