MY IO-375 from Aerosport has ECI jugs and I think the most telling difference between these and other brand cylinders is the fact that the fins taper down from mid jug to the bottom, forming a conical shape that does not fit vans cylinder baffles very well
Maybe there are some other way to tell?
They also sell cylinders with a "normal" fin arrangement.
I would think there should be a S/N or part number etched or stamped on the cylinders. You should be able to trace that number to the manufacturer.