I think that vandalism is a valid concern and it also leaves the vandal open to punishment as the sticker is evidence of "wrongdoing." I do however like the shock value of a sticker. It's a bit reminiscent of The Scarlet Letter though.
As another commenter posted out above, some folk just aren't receptive to polite requests not to be an asshole. In these cases, I fully endorse public shaming.
Who said it would work? I just think unrepentant assholes deserve to be publicly shamed.
I don't think we're dealing with unrepentant assholes here. We're dealing with inconsiderate idiots. "Never attribute to malice that which is adequately explained by stupidity." I know I've hurt people out of stupidity my share of times. St. Bernard of Clairvaux once said the the cardinal virtues are "humility, humility, and humility." When we see bad things in the world, we should try to correct them, but we shouldn't automatically assume that the people doing the bad things are always bad people. That is, unless we're all bad people too?