A friend of mine and I every week take a stack of index cards and write on them in large letters “Practice Modesty,” and when on the train or walking in the city, we’ll quickly hand these to a pritzusdik-dressed woman, whether frum-looking or not (goyim get the English, and frum-seeming women dressed immodestly get the card which says “Practice Tznius”). We have never been attacked or given a hard time. People take them, and G-d willing, they hold on to it and think about what it says.
This doesn’t sit very well with me. I understand the thinking behind it, and maybe I can even force myself to cards being handed to frum women, but Jews are not especially loved by the rest of the world. Why go in their face to advertise that we are different than them?
Additionally, I’m not someone who wears short skirts etc, but I don’t think I would appreciate being handed a card that said “practice Tznius” from someone off the street.