A @sit_place message on the character would be super! Appended to the stock line about what it's sitting on.
Yeah, I know people fake it with @look_place a lot, but, in places where there are actual seats (read: every place, there's always the floor) a @sit_place would support RP the same way @lp, @voice, and @sleep_place do.
Sometimes there are good reasons to have the character truly sit, when faking it with @look_place wouldn't suit the game mechanics. And I'd still like to convey information to persons having a look at the place, beyond just the info about what I'm sitting on.
Maybe just letting @look_place be shown in addition to the stock sitting message would do the trick. Instead of eliminating @look_place when sitting.