It seems the Seward Park Grammar Police beat me to this one.
Thank you for changing that adjective to an adverb! Seriously, what were those sign-makers thinking? It's not a bad idea, though. "Drive Nice(ly), It's Contagious." Apparently Seattle has "Drive Nice Day" once a year. I think they should change it to "Nice Driving Day." Read about it here: http://www.driveniceday.org/. You can get a free sticker.
I also like the added touch of the exclamation point. Drive nicely, everyone! (and not just once a year, please.)
