I wouldn't describe it as "unsafe". It's neither. Locks aren't dangerous. There is a whole level of subtext going on there and if you are in on it (which you seem to be), then it makes complete sense. If you are not, it leaves you scratching your head (as I was). I will argue that it is completely ineffective wording as the only people who will understand what it means are the people who don't need to read it.