I used to work in a building which also housed a crèche and an after-schools club for older children. Someone put up signs in the bathrooms about not using "alot of toilet paper". I took them down and replaced them with signs about not using "a lot of toilet paper". About half the people who noticed me changing them couldn't see anything wrong with the original signs! I pointed out that that was exactly the reason I was changing them, so that the kids didn't get the wrong spelling reinforced in their minds.
Similar to the "Registeration" story, a local upmarket hotel had "Enterance 100m" on its sign for months a couple of years ago. They eventually changed it.