it was changed last patch from "/display main hand" to "/display mh", the lodestone probably just wasn't updated when the patch dropped. There are a metric ton of places on the lodestone that have not been updated ever, take this page for example:

http://lodestone.finalfantasyxiv.com...5e1bf4ab725f29

or (holy crap this is old) this one:

http://lodestone.finalfantasyxiv.com...dc6c3c15d8fab3