Radiators in public places used to have warning labels in three languages that you were not allowed to put stuff on top of them, because it could catch fire. Those radiators got hot. (And a generation of Swedes learnt how to say "Do not cover" in Finnish. Finnish is completely unrelated to Swedish, and like most Swedes I only know how to say "Thank you" and "Good morning" and "One beer, please", and a couple of other things in Finnish. And, of course, "Do not cover".)