I found this in a bathroom of a Taco Bell near Sutton, West Virginia. Not only is it misspelt, but there is something wonky with the logic here. Why should I be courteous and lock the door? Isn’t the social norm that people knock before entering a bathroom? Granted, they would assume it’s a multiperson bathroom in this case, but a sign could be put on the door: “NOK FRSIT.” Also, doesn’t it seem to assume that you won’t mind much if someone barges in on you wiping yourself, but that the barging party will? A better sign would remind you that you need to lock that door.