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This three-sided pole on an airport tram
(sh.itjust.works)
I had never seen one of these before today. They're great. Way better than reaching for a single pole in a crowded car and wrapping your hand around some stranger's fingers. And If you have the whole thing to yourself you can hook your arm through it.
I just saw that the OP said Seattle airport and that's plausible for me. I'm going to choose to think that was it and save myself the mental agony.