It means the pax has been checked in and has bp's to his final destination.

Like everything else about "OneWorld" it's up to the whim and/or skill of the check-in agent whose desk you're standing at. Once BA at LHR could not issue bp for a cnx to IB at FCO (especially amusing since their signs all blaze 'British Airways / Iberia'), another time CX handed me bp's for the next four flights, including themselves, BA, and AA and was about to tag the bags until I pointed out a RON where I'd want them.

IMO the 'gold' in this thread is the acknowledgement that OW is supposed to protect pax across separate tix. Alas no self-respecting agent will give much credence to "I read it on FlyerTalk" - it would be nice if the poster could provide a jpg or something of the original correspondence from OW that we could all carry around in our passport case.