It's a figure (or a physical model I guess you could say). I don't know much about them, but I think they might have been used as reference for Sonic's design. I believe this was used as the direct reference for the Sonic CD title screen model.
Right! The figure used for the SCD title screen that was posted a while back. Thanks jogging my memory.
It's not a bag, it's the Blue Gale jacket from the Mary Garnet origin story for when they were making Sonic 3. I talked about it with Ohshima some years ago when he reached out to ask about stuff from my collection. So I took the opportunity to ask him about it since I knew fans were going to be curious about it. When I asked him if he drew the emblem/plane nose art he said: Not sure where that fansite got that pic. I imagine it has to be something Sonic Team posted since the jacket and one of the figures they made for Sonic CD are there.