I like this idea very much, and propose to take it farther: the code LOCK will lock any open station.  Making it easier to lock than to unlock seems wise to me.

[Subrincinator] Are “open” and “unlocked” not the same thing?

[Kevan] We have defined locked stations, but we have not defined stations which are not locked.  If there is a difference between stations which have been previously locked, and those which have never been locked, then the former would be ‘unlocked,’ in a broader category of ‘open.’  I’d prefer not to split hairs, and to say that “open” and “unlocked” are the same thing.  But until we define it as such, is it safe to say this is so?

CoV I prefer just LOCK as command

CoV per Ely.  If LOCK passes, this is redundant (which is in the spirit of Mornington Crescent, isn’t it?)