“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.”
I think that’s a great idea. But I would limit it to yidden. I wouldn’t be worried about what oomis is, no one would mistake it for that and besides it isn’t against the law, but why waste your time on goyim when you could do so much good amongst yidden? Keep up the good work and hatzlocho.