Basically we need to come across as normal nice people. I don't think it will matter if you dress casually or in suit and tie or if you wear the T-shirt.
I think being viewed as
Brother or Sister Df'd, I hate this Freakin' Cult
is the look we want to avoid. If the ordinary JW or even the world sees us as people with a chip on our shoulder we lose credibility. Remember their misinformation campaign is that Bill, Barbara, Joe etc were actually disfellowshipped for wrongdoing and we just want to do whatever we can to dispel that image.