Actually, we've never had room service while on our three 10 day cruises even though we have it frequently if traveling where I have to pay for it. Go figure.
Anyhow, we just leave the tray/dishes in the room if we're only there one night, they're breakfast dishes and then I leave a separate tip for whomever removes it from the one I leave for Housekeeping. If we're there more than one night and they're from the evening meal, then we'll call and have them removed. If room service didn't respond relatively promptly, especially in in a case such as the Captain's, I'd make a reminder call(s) until it was but I doubt I'd ever leave one in the hallway, especially aboard ship. As Fern so aptly pointed out, hallways are far narrower on a ship and therefore, especially out of common courtesy for fellow passengers, I wouldn't do so.